Of course they can.
If suddenly it's at 12% then you can borrow less (or you live in some place where mathematics does not apply), and conversely if it drops from 12 to 2 you can borrow more.
Maybe not YOU, but you as in the general population. You have just never experienced it, as you have to go back to maybe the 1980s to find those expensive loans.
All countries have laws and rules based on income and whatnot, the usa is not exceptional.