Fear of losing re-election.
Which is why he kept flip flopping in 2020 on the covid issue, unfortunately he was relatively green to politics as a businessman and while flip flopping often works as a CEO well it doesn't work as in bent POTUS or governor or any other executive. He needed to pick a side and stick to it firmly.
It's also why he waited until his second term to implement some of his hardline issues. He's gonna be on a yacht somewhere in 2029 and playing golf no matter whether his approval rating is 80% or 30% nationwide at the end of 2028, so he doesn't care now.