Trump is probably on the list, so he has to protect that. The Democrats had it during their entire presidency; even if they didn’t want turmoil during their time in office, they could have released it after their presidential defeat and before Trump took office.
It’s likely heavily reinforced by your voting system but 2 party systems aren’t unique to that system, even in theoretically better voting systems you frequently end up with very similar results. Australia as a case in point. That said if current electoral trends continue we could be seeing the end of that here and at least our system theoretically allows that to happen.