Ocean Monuments are impossibly rare

I was looking for some ocean monuments to add to my list of coordinates for a specific seed, but I searched for hours and could not find any ocean monuments whatsoever. I was expecting to find at least one, but no luck, even when I searched in a 8000x8000 block area centered on (0, 0). Only when I created a custom world with the biome set to deep ocean could I find any ocean monuments.