For the purposes of framing your question, are you meaning:

• commit to a single person in a monogamous relationship long term?

or

• commit to a legal construct of a relationship such as marriage?

There are different answers for each.

Anyone who is not cautious in choosing a partner for the next 60 or 70 years is nuts. This is probably the most important decision you will ever make. We are almost 30 years in and it is great but it was not easy to find someone. Not sure it is comittment exactly. More finding someone that wants a long term partner and that you both like each other and can stand each other and are heading in a similar direction in this complex world.

I mean, in my own case, I’m such a bloody mess I couldn’t really recommend someone be in a long term relationship with me. Or nothing too deep, anyway. I’d feel like I’d drag them down. But all that aside, the biggest reason I can think of to be hesitant about commitment is that, in commiting, you will find yourself having to give up control of your life at times and making comprises for the other person’s sake. Where as if you are non-comittant, you will have more autonomy to lead your life how you wish.

Because they don’t like their partner that much. They want to get someone better in the future but don’t want to be alone now.

If they’re truly “afraid of commitment” and not just horny, undecided and exploring their options, it’s because giving yourself entirely, caring for someone that much and finally changing your identity to being part of something bigger than just you can cause a lot of grief if something goes sideways (I mean, death is a promise and all but that’s more digestible compared to being broken up with, specially if it comes much later in life) and some people are very afraid of that potential result.

Do they fear commitment or just not want it. Commitment is great, but it’s hard and a lot of effort and it changes you. Some people fear that, some people reject it not out of fear but because they don’t think that they’re ready or that the value proposition holds up for them.

They aren’t where you are in life right now. Maybe they never will. Whatever. You can’t put your life on hold waiting for someone else.

Most people afraid of commitment are young. It’s because they want to experience different people before settling down, eventually finding “the right one” but like when they’re 30+ but some people want to commit and have children at 20.

Maybe it’s an age thing? Like when you’re dating as a teenager you know that your brain will still develop and you might grow incompatible with your partner, so it’s hard to invest in the relationship if you’re unsure on whether it might last?
No idea though, people say I’m a bit too utilitarian when it comes to dating.

Bad relationship with their parents in their childhood taught them to be afraid of being in a close relationship. This is both extremely messed up and tragic.

Because it’s often real fucking scary? My every past (often futile and misguided) attempt at forming a (stricly monogamous cishet) relationship ended for one reason (me) or another (the other half). I have been hurt by myself and others, by my own feelings or the other’s or the lack thereof from either. Now I live together with an incredible woman who gets me and I get her and our future’s have so far seem well aligned and stuff and I never have to fear to be judged or ridiculed by her unlike previously and I know she trusts me (and I trust her when she says so) as well. And yet still I find myself fearing: what if she’ll just stop loving me because of xyz? Because everyone else has left so far (sure I might have personally driven away a few because of my fears and insecurities, and maladaptations or other toxicities, but I’ve grown from those times emotionally). It’s real scary to open your shell and be at your most vunerable, but it is also required. Not everyone can be expected at any point to be able to do it like that.

That’s my two cents.

Because people do not want to be committed to the wrong person. They need time to asses the other person of the relationship to judge if they can commit.

For women: Because they already know the current partner isn’t what they want. But they don’t want to be alone while they look for the next upgrade.

For men: Because they prefer to explore the many potential partners available to them to a single partner.

Sometimes you get your heart broken by who you thought was “the one” and it becomes hard to trust it again because “these are the same feelings as last time and look how that turned out.” Even if you want to, there can be a “fool me once” element to it that isn’t so easy to shake.

And for me personally so far it’s that everyone seems to expect me to fall in love within a month and marry them within a couple years. Bruh I’m slow at that shit sorry idfk what to tell you and the more you pressure me the less likely it’ll ever happen because it’ll push me the other way.

Modern dating has zero expectation of marriage and the direction of the relationship is rarely discussed. So the person who is least committed in the relationship holds the strongest position.

Keeping their options open. Ive had many conversations with people who have a long term relationship but they never married and they insist that it’s exactly the same ‘just without a piece of paper’.

No, it’s not.

That piece of paper isn’t the only thing that’s different. The difference is being 99% committed or 100% committed and it’s “only” 1% difference but that 1% is a huge difference.

100% committed means I’m not scared to marry you because I want to be with you the rest of my life. That means I’m here, I’m 100% for you and no one else no matter what happens. Not ‘til the feeling goes away’, not ‘til you dont turn me on anymore’, not ‘til someone else intrigues me more’, not 'til you dont look like you did when I met you, not ‘til you are more work that I thought you’d be’, not ‘til you get sick’, not ‘til we’re not having fun anymore’… I’m here TIL I DIE, come hell or high water, good times or bad. 100% committed.

And when you find that kind of commitment, a relationship finds its groove and you can start to relax and really enjoy life together. Because you know your spouse has no plans, no desire, not even any thought of going elsewhere. THAT’S what makes marriage and 100% commitment the most fulfilling and most satisfying relationship.

I don't know if it's so much fear of commitment than it is just trying different people and everyone is allowed to do that whether they like it or not. Sorry, that's just the dating world in practice. People only have one life to live and they will take all of the time of it, to find someone or not, whether it means having to go through multiple people.

So I find it a bit misleading that you use the idea that it is all about being afraid.

Also, your ex did you a favor and was at least honest. That's far more mature than anyone who simply just won't give you that clarification. What it meant is that you weren't exactly 100% up to par with what she expected or who she looked for. You were probably a modest percentage to warrant being liked.