Here's the thing: if the Republicans invoke the 25th Amendment against Trump, they might never win an election again. And they know it. And it terrifies them.
Trump won the election with help from white supremacists and other assorted garbage people. That's not his ENTIRE base, mind you - the rest were mostly lifelong Republicans deadset against letting Hillary win - but I do believe the deplorables are what put Trump over the top.
Garbage people who otherwise never would've voted were the difference between Trump succeeding and Romney failing. And Trump can still travel to Bumfuck Nowhere and fill stadiums full of these fucking people.