You can run for president from in prison! In fact I think that’s one of the more important rules intended to curtail political corruption that are still left. Otherwise every republican candidate from now until forever would be looking for an excuse to jail their opponent from the beginning of campaign season.
You cannot, however, run for president after being convicted of treason against the United States.
Because of money!
Every time you see something that feels illegal but isn’t, or that makes no sense in general, look for the money trail. There’s always one, and it always leads to the explanation.
In this case, insurance companies have made such an absolute ass ton of money by killing off their customers that they have become a political entity. They now use their deep pockets to lobby politicians to keep their scam legal.