[QUOTE=jjimm]
It was known and declared to be the final season. Merchant and Gervais have a fear of jumping the shark so got out quick.
[/QUOTE]
They also stated that they’d simply run out of ideas for the characters. However, I have recently heard rumors that they’ve been talking about going back and doing more, because their work on the American version has given them new ideas. Honestly, though, I’d be surprised if it ever happened.