He’s openly disrespectful, emotionally unavailable (or inconsistent at bare minimum), unfaithful and he has few real friends or ambitions besides sitting on his couch and doing drugs.
I honestly can’t tell if he’s attractive or not (although he’s clearly out of shape); he’s not exactly stupid but he’s clearly unwise and extremely irresponsible.
What does she in this guy? The only good things I can see him as a romantic partner are money and fame and she doesn’t seem like the type to obsess over that.
This right here.
To use a personal example: me.
I’m fat. I’m also ugly- like, “my torso is lopsided and lumpy from the time I fuckin’ died horribly” levels of ugly. Like, the state gave me a Disfigurement Rating to serve as mathematical proof of how fuckin’ ugly I am. On top of all that, I’m also bald, yet at the same time hirsute, and covered in scars that if laid end to end would be taller than I am.
And precisely none of these things have ever prevented me from finding a partner, sexual or otherwise. For a man my age, in my country, I’m significantly above the average number of partners. Being “in shape” stops being important pretty much the moment your brain stops being in Horny Monkey Grabby Hands mode.
Bojack got his start doing comedy, and chicks dig a guy who can make them laugh. He’s also intelligent, and speaks eloquently- both are things that likewise draw people. On top of that, he craves validation to the point that he seeks out people who have “people pleaser” personalities- and when someone who people pleases and someone who craves being people-pleased connect, it’s a feedback loop where each person’s shitty behavior reinforces the other’s.