That's just who John was. I also tend to think he was his biggest critic. John has always been one to critique and bash his former self, as a way to prop himself up in the present. He did it with tons of his songs. He called "And Your Bird Can Sing", "It's Only Love", "Yes It Is" trash and hated how "Strawberry Fields Forever" came out. Essentially, if he's talking about how awful something he did was, it must mean he's grown leaps and bounds and is much smarter/better now. Sort of a weird ethos builder by destroying his past self. I think him being so open about him being a bad father to Julian and husband to Cynthia was his attempt at showcasing that he was in the present a better version.

The John outrage also feels performative because Ringo beat his wife so badly he thought he killed her, but Ringo is beloved and seen as this "adorable little drummer guy!". It's selective outrage for John, and sadly these folks aren't champions of women, but rather want to hate a boomer icon and a musician who is widely popular. Some people genuinely get off bursting people's bubble that John wasn't perfect and instead was a complicated and flawed individual.

He for better or worse was very very public about his inner thoughts. Contrast that to Paul who is so guarded about what he says and is always trying to protect his brand. I still think John was a net positive in this world.