Ok, so hear me out. If we assume that time travel is possible, any changes to the timeline have to have some limitation. To whit, they can't end up precluding time travel, both for the practical paradox avoidance, and also out of some sense of self preservation.
And there's only two plausible scenarios given our current state of the world where they develop time travel. Either the future is so amazing they have the capacity to experiment and make it, or a billionaire creates it to be rich.
One doesn't need to change things, the other doesn't want to, either.