One problem is that we are quite restricted from speaking about anything that might be considered "religious" and/or "political." Lively debates need lively topics and with those two branches of discussion off the table, and most others too often moving into those two, there is little chance of there being much to discuss or any discussion that can be discussed for any length of time.
In the end I would say that lively debate doesn't take place because the forum moderators are rightfully afraid of it. People don't really know how to debate civilly and thus they have little opportunity to practice here.
Just my thoughts.
AJ