Hm, well, you actually could store higher values in a Float (Number) without losing precision, because Number is a 64 bit value, but int is 32 bit (I think).
However, Flox really just stores integer scores, and it's not possible to work around that. I don't think there's a specific reason we implemented it that way — I think we just thought that the integer range would suffice. :-/
In my opinion, though, it makes sense to limit your scores to a smaller range, anyway — many players won't even be able to count so high. And you won't need so much screen space for your text fields. 😜