There is a topic about this:
In short, you aren’t actually nominating a Pokéstop, but rather a wayspot that, if accepted, gets added to Niantic’s Lightship database. From there it may get added to Niantic’s various games, but each game has its own set of proximity rules that determine whether this can happen or not. If you want to learn more about the system used by Pokémon Go, read this article.
If you want a visual representation of why they don’t appear in Pokémon Go, please feel free to provide the names and coordinates of your wayspots.