There are many advantages of being an incumbent when running for office. There is also one big disadvantage. There is a record. Not only of the policies someone like Trump passed, but the people he has appointed. When judges he appointed make radical, unpopular decisions, that reflects upon him and shows the type of judges the voters can expect from the candidate. Candidates also make other appointments like Cabinet positions, but also thousands of sub-Cabinet level positions. So when many of those appointees then go on and create a plan to kill the Department of Education, each of those appointees are often identified as a "Ex-Trump administration official" (and probably future Trump administration official). Their policy becomes Trump's policy.

Project 2025 has been created by Trump's people and fits his record and is unpopular. Make him wear it.

I know Trump is not the incumbent in this next election, but he has held the office so the point still stands.