The series is not without its shortcomings, but the draw for it is similar to Mario games, as the mechanics base themselves off of platformers primarily. There are many who can't enjoy Smash bros, but wreck people at Street Fighter and Tekken because those games are more muscle memory, and involve zero platforming. Or are Counter Strike legends that can work every spawn point and territorial advantage in a map.
Lots of these hyper-competitive fighting game players tend to talk shit about how good they are at games, and get completely obliterated by the first Mario stage. But they can focus cancel and combo into Ultras, or no-scope hapless noobs across a large Battlefield map.
So, it's understandable why people wouldn't understand the fun in Smash Bros. Platformers aren't exactly the dominant form of game lately. By the same token, if you were presented a book that you'd like, but it's in Thai, and you don't understand Thai, you're not going to get anything out of that book unless you took the time to learn the language.