Probably because it's hard to link a suicide to a specific cause. And even if it is (eg someone left a message to his spouse), the reason is probably not going to get out often.
Also, other factors on top of my head that might influence it:
-not every wife is going to want to check the list, and I guess most people would commit suicide only once they've been discovered.
-it's not really easy to access the list, I think you have to download it from some torrent. So to be discovered you need a wife who has a doubt and want to have a look, plus have the knowledge to do so.
-some of the accounts are probably fakes.
-there's the "easy" excuse of "someone else created an account for me! I think it's that guy at work that hates me". It's probably true for quite a few people too, it's an attractive target for a revenge/prank, just like gay porn websites. I think Obama's email address is in the dump for instance