> Why does it still exist?
Same reason that this place still exists, I suppose. A community has developed around it, and it's become a hangout of theirs on the internet.
> Who posts there
I don't bloody know, m8. A range of people. Like here, they have their own unique namefags. Though there is some overlap in users.
> Does anyone still think it's a good site anymore?
Depends on who you ask. Most people here seem to think not, but regular TC users probably find its culture enjoyable.
> Is there an upper limit for how many years sad cunts can continue posting the same stupid schtick?
None has yet been found. Experts have compared their persistence to that of a machine. So as long as they have the opportunity to do so, they will likely continue their behaviour indefinitely.
(Edited 7 minutes later.)