> "Why not just eat food?"

Why not just do [less convenient thing] instead of [more convenient thing]? Well, convenience, of course.

> "I've never really understood"

You only need to understand that different people can have different priorities and desires.

> "the obsession ... glop ... stuck on ... why not just"

All you're doing here is using negative framing to pretend that your own priorities are more real than someone else's.