Because he actually has gotten more done than the past 4 or 5 Presidents did in their first term? It's not hard to understand. Plus neither party has failed to renominate an incumbent in recent history.
The better question is why would Republicans nominated Trump when he clearly has extensive cognitive problems, has been indicted multiple 91 times and has caused a realignment in previous Republican strong holds. The country would be better off if Trump suspended his campaign, but clearly that's not happening. Biden is not the problem, Trump is. What even is the point of this thread?
He did not get more done than George W Bush in amount done. In W's first term he got his tax cuts passed, his education bill passed, medicare part d passed, the farm bill passed, partial birth abortion ban passed, and his entire foreign policy/national security agenda passed as well.
Congress pretty much was more deferential to W than they have been to any president in decades and W 100% got more things done than Biden has in his first term.