I've been on the other side of it, and your approach can come across as childish, like arguing with your math teacher that billy couldn't have eaten 4/6 or 2/3 of the pizza because he'd get sick.

It's a _hypothetical_. The problem needs to be constrained because realistic problems often either 1) have standard answers that don't require real thought or 2) are too hard to solve in an interview. Asking how you'd solve some problem on a CPU that doesn't support multiplication or something shows whether you have skills that could transfer to solving real problems but can be asked more quickly.