I'm not that well versed in Family guy's chronology, but was this after or before the entire cast became irredimable psychopaths?
I mean, as bad as jerkass Homer was (is?), the flanderization of a series that goes for so long is somewhat understandable, the term does come from the Simpsons after all, so jerkass Homer and insufferable Lisa are somewhat understandable given the long running time.
But Family Guy is different, the whole show is just mean spirited as fuck. And not in a really controvertial, shock jock way, or trying to have some sort of commentary, the show and it's characters just seem to hate each other and are horrible people.
And I heard that is the "voice" the show found, since it was never any good at being a family sitcom like Bob's Burger or King of the Hill, Family Guy always sucked so the show runners said "fuck it, we ain't gonna win any hearts or Emmys here, might as well just be assholes", and it ain't like McFarlane gives a shit, as long the checks keep being on time.
Still, I don't think the decision to make Family Guy's character vile pieces of shit is due public rejection, because at one point the show was way more popular than the Simpsons. Sure, it was always taken a sloppy knock-off that relied too much on cut-aways gags to get some laughs, but it had it's fans.
So what the fuck happened? Whenever I see a new family guy episode, it is just fucking bitterness made cartoon, Peter is a irredeemable monster that is hard to stomach for 5 minutes let alone a full episode, and it isn't like this is some commentary on how horrible it would be to deal with a cartoon dad like the Simpsons did with Frank Grimes, no, the Griffin Family just hate each other, and the show just hates.