Because
A) the cat is in here asleep (most important, DP would not disturb a sleeping cat)
B) I'm 39 weeks pregnant and feeling very lumpy
C) I have already hoovered the kitchen and hallway
D) hoovering is meant to be DP's job anyway (he bought the hoover he wanted for this precise reason...)
E) I want to sit on my arse for the rest of the day eating and watching crap TV until school pick up time?