There’s also the fact that a lot of the better players that bothered with ranked are now mostly S or above. Back when the game released (and for about a month after that), you could still find plenty of good players around B~A rank.
Since they’ve all moved higher (or don’t play ranked at all, or used to but don’t anymore), the vast majority of the remaining people aren’t as good. So there’s more room for people who honestly aren’t all that good to get all the way up to A. The ranking is really just another way of displaying win rate: it doesn’t account for how good you are or how good the people you beat were, only how often you won in general. The way it’s structured, you can’t use it as a measure of skill at all.