Half the reason, at least for me, is that a lot of the levels' names are just completely random things I come up with on the spot. Unless the level takes a lot of testing effort, or stands out in some way, or ends up being really popular or one of my personal favorites, I'm not going to remember it. For example, I received a PM a while back talking about one of my levels called "Back And Forwards We Go!" - I had to think for a while to remember which level this was! (It's Trial 2 of LPII Bonus Pack)