My take:
1. Apathy. The Bible or 'spiritual' things have little relevance in a JWs life anymore. Following Organizational procedure ("listen, obey and be blessed") takes priority over everything; blindly follow WT and you are golden. Who needs the Bible? People generally do not have a problem freely talking about what really interests them. The fact that JWs talk very little, or not at all, about the Bible speaks volumes. You don't talk about things you're not thinking about. Period.
2. As others have noted, "Bible discussions" are nothing more than regurgitating what has been printed in a magazine. Not very interesting (and most likely few JWs have actually even read the magazine anyway. Nothing to discuss).
3. I also think there's a growing number of JWs who secretly do not agree with WT. I recently heard of several long-time JWs mocking the stupidity of ToMo's "Spanx" rant. It's a revealing attitude from these JWs toward someone who's allegedly anointed and a GB member. If JWs really believed that they wouldn't criticize good 'ol Tony at all.
4. Bringing up an honest Bible discussion (or anything else WT-related) would most likely result in disagreement with WT, which sends up the JW red flag of apostate suspicions. Why go there?
5. The new replacement for the Bible: jw org. The JW Golden Calf. Why open a Bible or even discuss it when you have a website?