What these all have in common is the refusal to admit that the people who they claim to be jealous, insecure and unreasonable might have more right to own horses than they do. April doesn't want to see that she's being a dog in a manger, Mike won't face the fact that Lizzie is just as much a victim of Elly's inept parenting as he is, Liz doesn't want to admit that huffing and puffing about how other people are moving on while she's standing still is her own damned fault and not that of EEEEEEEEEvil career women, Elly can't face the fact that most of what's wrong with her kids is that they've a fool for a mother and John can't see that he's mostly unfair, unfeeling and unkind. To do that would mean admitting that they don't have the answers and should probably take a back seat to people who know what they're doing.
It seems to me that this sort of mentality is a response to Lynn's fear of not only being replaced as the author of the strip but being surpassed. While the two of them have superficially similar styles of art, it doesn't take too terribly long before you realize that she'd have been able to avoid falling into some of the more ridiculous traps Lynn does. Gone would be the disembodied heads, the dot eyes, the oval noses and, yes, even the Patented Patterdander. We'd also have to deal with the fact that Ms Matchette probably doesn't have the same hang-ups as Lynn does. Gone would be the poor pacing, the zits-and-vacuuming, the endless whining about the evils of children, technology and rabbits, John eyeballing everything in a skirt while Elly's watching and, yes, no more whining about how Elly will only ever be praised for her hard work ten years after she's dead.
Lynn was thus not only worried that she'd lose control, people would be glad of it. This fear of not only being replaced but being mocked for standing in the way leached into the strip and turned the Pattersons into the mowers of tall poppies.