It's partly because a large number of people smugly hold such a simplistic, stupid and completely unreflective view of the guy and the political/social currents he's both ridden and manipulated, that he has been able to get so far in politics. Trump is all kinds of unpleasant things, but a screaming orangutan of rage and stupidity he isn't.
Even as it stands, his entire political career since 2016 is a very unique chapter in U.S. political history, which will be judged as such in many complex ways across the coming decades. This is not simply the result of an incredible number of coincidences favoring a complete, screaming idiot.