Didn't know I was called here, haha.
Mine RECENTLY started eating off the bottom. No real explanation...I added a couple smaller plants and he seemed to like playing down there. The next accident involving a falling pellet including him actually NOTICING it (30 minutes later, haha...) when he went back to his play-pen. Now he occasionally scavenges the bottom.
But other than that...it's possibly instinct? When in doubt, point fingers at instinct. Haha.
"Hey. I have some bad news, and some good news."
"What's the bad news??"
"There's no good news."