See, this makes me think one of two things: Either she couldn't make anything more complex (or couldn't be bothered to.... Take your pick), or she knew it was "good enough" for her kid, and didn't care to spend any more money on making him a "pizza". Because let's face it, a slice of bread, a slice of cheese and a squirt of ketchup is really inexpensive. The most costly thing there is the slice of cheese.

Rich people can be cheap... In fact, that's usually how they become rich.

I guess incompetant chef, and anything made with love and novelty makes kids love it?

or SHE was poor and kept that food habit?

or it's just a quick and easy snack that tastes good that used a linguistic shortcut