It's not liberal programming in the sense you're trying to define it as - it's television and comedy.
There are PLENTY of liberal messages in FOX programming, regardless if it's comedy or not.
From wiki: Politics in the Simpsons
"Some U.S. conservatives have voiced opposition to the show"... I read that far.
From wiki: Seth McFarlane
After criticisms from the Parents Television Group... (a conservative activist group)....
"Family Guy has been cancelled twice, although strong fan support and DVD sales have caused Fox to reconsider"
So despite conservative criticisms (there must have been reasons they were criticizing) the shows remain on FOX because of the money.
I just hope the same people that watch these shows don't watch FOX news at the same time. (they shouldn't be allowed to, lol.)