Because they’re not disabled. What are you even talking about?
That’s like supporting some racist segragationist bullshit by saying “well, can’t black people just use disabled bathrooms? They’re a small portion of the population.”
See how ridiculous that sounds? It’s not disparaging to disabled people to point out how inappropriate that is. You’re just making life harder for disabled people to feed some asshole’s bigotry.
We need better stalls in the US for that to be the case. WAY too many gaps and openings.