Aoc can’t run until next election, Michelle Obama has zero interest in being president (didn’t even want to be first lady), Elizabeth Warren isn’t much younger than trump and Biden (and a lot of moderates still won’t vote for a woman, see: Hillary Clinton), and Jill Stein is just as old too and part of the green party which isn’t going to even have a chance at winning a presidential election until there is no climate left to change unfortunately
None of the stuff they’re doing yet is stuff that can be blocked by the president, most of it is happening in right wing courts and the supreme court that Trump/conservatives rammed a conservative majority into
If trump gets elected there are more things he can push through, and they won’t have to worry about a veto if they try to pass an actual law rather than using court rulings. Republicans put a lot of time and planning into this project 2025 planning, it’s not just some ultra right winger dudes in a house throwing stuff together, it’s a lot of political and legal experts working together and putting a lot of time and effort into planning these things and figuring out how to force each of them into existence in ways that can’t be blocked or stopped
I don’t like Biden and would prefer basically any other left candidate, but if Trump gets elected there is a lot more that they can do without fear of it being blocked. That’s why they’re not doing all of these right now, they’re just getting things in place to do them day 1 if Trump gets elected