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 when certain thresholds are crossed.

  • 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.