The "glop", as you put it, is also food. It has the same nutritive components and addresses the same hunger signals and fuels the body's same energy-production requirements. You just don't like it.
None of your complaints make it not food. They just mean you don't know how to differentiate between your personal subjective preferences and correctness and it makes you sound snooty.
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.