I think it's not necessarily the number of villains but how villains tend to be approached nowadays. Nowadays it is common to portray villains as not really bad guys, usually this results a diminishing of the character.
Take Thanos in INFINITY WAR as a recent example, in the movie Thanos is on a crusade to save the future of the universe by killing half of all life; he's not really a bad guy, movie-Thanos just has a plan to do some good that most people disagree with. Contrast that with Thanos from the comics, he's in love with Lady Death and Thanos's efforts to cause death and destruction are all for drawing Lady Death's attention & affection.
Heath Ledger's Joker is a popular rendition of the villain because Christopher Nolan does not seek to explain the Joker, nor give him a heart touching character arc. Heath Ledger's Joker just wants to watch the world burn.
I've not had a chance to see Spider-Man: Into the Spiderverse yet, but Ialready have a notion that villains are truly villains, truly bad guys in the movie. Wilson Fisk and the other villains in S:ItS need no other motivation than their personal quests for power, wealth, destruction, and maybe even revenge; and they're not lesser characters for not having backstories reveal how they're not really bad guys, just misunderstood.
Who knows what evil lurks in the hearts of men?