If you have perfect knowledge of the future and know which stocks will do well, why bother with trying to diversify your portfolio to try to mirror the market?

So, as it turns out there are a few big reasons.

• it's a cosmic felony
• causing improbable events creates a new timeline which increases entropy in all probable realities, which can have some drastic (and usually negative) effects.
• most time travel agencies (which is what most people can afford) use technology that doesn't actually allow for free will, that's why it's mostly sold for vacations. You can alter/push some decisions, but for most people it's not gonna be successful stocks.
• • older technology was advanced calculation in a realistic simulation. Most people just wanted an old memory or to get closure. Some people just try a different meal or movie choice, the experience is all that matters.
• time mercenaries. We're actually not sure who these guys are, but we also don't wanna know either. Some say they're who cause spontaneous combustion and embarrassing deaths.
• most forms of actual time travel leave the user stranded, with chronic or terminal illness (and sometimes amnesia), and in some cases fading/poofing out of existence.
• • On top of that, new timelines of you typically aren't experienced by you. It's a different you. So that was nice of you.
• time spiders. You don't want to know.