Because, after playing since 2004, the game still has its addictiveness and thrill.
For the money reason..... It would be fun to give away. Just today someone gave me 300,000 GP, for no apparent reason. My only reason is good karma. The day before I was dropping stacks of 5,000 GP in fires, just to see who would see the money first, and who is really paying attention. I also dropped 2gp, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192..... all separate stacks to see who would get the money at the end. Really, I feel like I should win the money because I give quite a bit of it away to people who really play the game, or are trying to reach a goal. Not someone who is just standing there, begging for money at GE.
Oh, and I'm trying to get some cash to raise my firemaking level.