No kidding. When I zoom in on a few square miles around my house and ask to see restaurants, it shows only a few of them even though there is plenty of space -- it isn't like it has to prune some to make it readable. I zoom in and some appear that weren't there before ... why? There was room to display it before I zoomed in. Gaaah!
I'd assume it's pruning to make only the best-paying (to Google) restaurants visible.
Oh wow I always complain about this, I didn't realize other people were also so frustrated by this. Tons and tons of cafes by my house, but I zoom in with about a six block radius, where there are at least 20 cafes or cafe-restaurants there, and literally 1 or 2 come up.