Part of this is because to my understanding, intro economics classes tend toward right-wing conclusions (like minimum wage & rent control are bad) whereas higher-level economics courses take a lot more variables into consideration.
What happens to some successful economists is the god-complex. They imagine clairvoyance and power they don't have, which makes them willing to gamble societies well-being to prove a point about their school and their abilities as economists.
Perhaps we have reached a point where min wage could be increased without substantial job loss, but why would we gamble with societal utility to make a pointless political statement about 1960s Keynesian economics? We have much better policy tools that require the government to insure domestic tranquility and promote general welfare, rather than lazily dumping those responsibilities on corporate America, as liberals are wont to do.
Stiglitz and Krugman have the god-complex. Some right-wing economists have a proclivity to worship free-markets as a sort of god, which creates similar societal outcomes, though the professional conceit is much different.