The BBC got burned on their last experience of a season of pilots (which is what that effectively was). They came out of it OK, with Being Human, but only after a near disastrous commitment to a season of Phoo Power (or whatever it was called).
Phoo Action and I still think it's shame that never got the full series. The other series in there could have been very interesting too, and interestingly it looks like one of them was reworked in to being "Hit and Miss" on Sky Atlantic which was a good show. Oh that isn't the last time they did a pilot season, they did one for comedy shows, which led to How Not To Live Your Life and Him and Her, I think, both very popular shows.