From what I have seen, it more stems from the activism vegans are engaged in more than the actual veganism.

I think there’s nothing wrong with explaining your ideas and why you believe them to those willing to listen, but I can see why pushy activism for any cause can get annoying quickly. There are often Jehovah’s witnesses outside my local supermarket, for example, but they only give you a pamphlet if you specifically approach them

The UK has a high rate of veganism, and part of that is attributed to the fact that the major vegetarian and vegan organisations in the UK generally recommend persuading people by offering them delicious food that is also vegetarian/vegan and saying it’s more ethical. On the other hand, the equivalent organisations in the US tend to lean more towards recommending telling people that eating animal products is unethical, and it’s difficult to accuse someone of unethical behaviour without being insulting. It also doesn’t help that multibillion-dollar organisations have run successful smear campaigns against groups like PETA - everyone’s heard of the time they took someone’s pet dog and killed it, but most aren’t aware that it happened once and gets reported on as if it’s news every few months, or that it was an accident as the dog’s collar had come off and it was with a group of strays, and got muddled with another dog, so was put down weeks earlier than it was supposed to be, bypassing the waiting period they had specifically to avoid this kind of mistake.