Deadpool is incredibly difficult to kill due to his healing factor, and the movie firmly establishes that with two scenes in which he regrows severed limbs. In the first of them, the masked mutant actually manages to reassemble himself like a crash test dummy after an explosive suicide attempt leaves him in multiple pieces.
The second time this power comes into play is after the Juggernaut has torn Wade Wilson clean in half. He's forced to regrow his body from the waist down. The results are hilarious and disturbing in equal measure, but they came with the consequence of rendering Deadpool's healing factor inconsistent throughout the story.
If Wilson is capable of reattaching all of his severed limbs, why did he need to respawn his legs from scratch? Wouldn't it have been easier and quicker to simply reconnect his bottom portion and spare everyone the Basic Instinct re-enactment?