"what would happen if everyone applying to these universities just opted not to check anything off? "
Well, you still gotta show up in person sooner or later in the application process to fill out further forms, pay your fees, etc.... and maybe some 'helpful bureaucrat' might just help you out on your form...or their own back-office forms....
That's after you've been accepted... you don't pay that stuff till you're registered. I suppose one can always check their own admissions records. The last thing people need is 'help from a bureaucrat' *LOL*