Why shouldn't you expect a problem's simplicity to correlate tremendously with how well it is represented in training data? Every angle I can think of tilts in

Why shouldn't you expect a problem's simplicity to correlate tremendously with how well it is represented in training data? Every angle I can think of tilts in that direction. Simpler problems are easier to remember and thus repeat, they come up more often, asd they require less space/time/effort to record (which also means they are less likely to contain errors).