I have a few theories in this topic myself, but could be there are other reasons?
1) The Casino game interface blocks the rest of the game, so when you go there you can't do anything else
2) A game in the Casino obviously require at least 2 players, but I can imagine that the first player there will not wait for very long for someone else to arrive (because of number 1 above)
3) Casino chips get really expensive, really fast, low level players have almost no choice but to use paid CC to get chips (perhaps this is intentional)
I think for the Casino to be a successful part of HCL something needs to change in order to get more players to go there.