I voluntarily dropped my rating to 1200 by skipping lot's of ELO puzzles. Now I'm presented with much easier puzzles and I've noticed that almost none of them are rated, because you have to have an ELO of over 1600 before you can rate. That way, simple problems will never be rated, because players can't rate them and thus, never be considered for deletion.
Suggestion: Instead of using a fixed threshold of 1600 ELO points before you can rate, you could use a dynamic system. For example, if a player's ELO rating exceeds the puzzles rating by over 200 points, the player can rate