Because what tards call pretentious is cool and blockheaded pandering to mass appeal gets uninteresting and lame after a while. It does not mean mainstream cinema is bad by default but it's usually the best when it pulls elements from shit people deem pretentious. Notice how the best blockbusters of the 80s-90s were made by either former New Hollywood people or by people pulling from New Hollywood. As well as "pretentious" foreigners. Paul Verhoeven started as an arthouse filmmaker in Netherlands. Milos Forman was making artsy social realism in Czechoslovakia.
Doesn't mean if a movie is "pretentious" it's automatically good btw. But retards who even use that word don't differentiate, just hate things above their level by default.