I don't know why Obama kept him around for his whole term, but the "White House Physician" is not normally where presidents go first when they need a provider. They go to the best people in the field...where Trump eventually went when, after he recklessly disregarded mainstream medical opinion, he not surprisingly became infected with Covid.
Other than that, I will just speculate that Trump brings out the worst in people pretty much universally.
As to the rest of your response, the answers are either contained within my post, contained within the links I included in my post, or have been thoroughly hashed over in the news or in this very thread so many times...LOL I can't believe you thought I would spoon-feed you the obvious! I do appreciate that you seem to grasp the general concept that replying is the right thing to do, regardless of the quality of that reply.