Mario is the most iconic video game character of all time and the Mario family of games are the most popular and widely played. I haven’t done research to back this up but I feel like this is just a given. It’s exactly because of the cultural phenomenon of Mario that Super Mario Maker 2 is so full of fun levels.
Mario fans know Mario games. We’ve been playing them for 30+ years. We’ve played hundreds of levels. Even Mario sequels are hugely popular and recognizable to people who don’t play video games. This basic cultural understanding and experience of Mario leads to the creation of so many good player made levels.
The very first thing I noticed this morning playing through random Super Mario Maker 2 player created levels were that they were all good. None of the ones I played were bad. All the creators clearly had a general understanding of what makes a level fun in a Mario game. Some of them were just okay, but they were still fun, because they still capture the essence of a good Mario level - verticality, well placed enemies, funny tricks, little secrets, etc.
It’s amazing that so quickly so many people can make levels that are just plain fun. Even some of the simplest levels I played were still kinda good. This game is fantastic and the fans are even better.