Also it's a lot harder to control MPs when they know their parliamentary vote doesn't matter so much. Big majorities usually lead to a lot of rebellions and factions developing.
I was reading today that Labour have been working on the possibility, and how to keep MPs busy. New candidates have even been having training that addresses the possibility that they'll get bored and spend too much time in the discounted bars!
Bizarre than the people who have most impact on our day to day lives, have one of the few jobs where it's acceptable to get pissed throughout the day.