Language is regional and fluid; words and phrases can come to take on meanings seemingly at odds with rules of grammar or logic simply by mass usage, and that's fine, so I think states can be justified simply because so many people use it. And the many people that use state are also not wrong.
That said, I think a lexical argument can be made for either term, partly because both words already have multiple meanings entirely distinct from their usage here. Where I grew up it was always states (and nationals), and I think the lexical justification for pluralizing both is that (a) "states" is essentially a shortening of "state wrestling championships" and (b) there are multiple championships at the event because there are multiple weight classes.
Accordingly, it's not the Stanley Cup Final, it's the Stanley Cup Finals, because there are individual events comprising the larger event. Compare that to Texas high school football, where the plural is rarely used, because it's only ever one game. Or the Super Bowl.