couple of reasons, firstly we can ban a members e mail address, they simply get another e mail address and re join under a different name, so the only way is to ban the IP address, thats where the trouble starts, as certain internet providers,aol for one, use the same IP address for more than one member, so us banning an individual, could infact ban 100's,
secondly, as has been seen lots of times, you ban one member, only to get multiple topics started titled, wheres so and so gone, wanting to know the ins and outs of a ducks arse, and slatting the mod who issued the ban,
top man stubb