doesn’t it seem silly to remove the leaves from a lawn, then buy and put down commercial fertilizer

I think you are imagining leaves from small and widely spaced trees. We do not put down fertilizer, but we remove leaves from the part of our yard we want to include grass. The parts of the yard we let the leaves stay kills all the grass (hardier plants grow there, but they are not compatibility with mowing to a walk-over height). Leaf mould easily takes two years to create, and grass needs sunlight in a half year from fall.