Your assumption is that the status quo provides those things. Nowadays, people will break up as soon as they get "the ick" or just have a rotating group of people they see. Lasting relationships are much less common than they used to be because it's easier to switch partners.

People just want to chase a local maximum of constant validation that they're pretty/smart/correct. They don't see or understand the value in working through fights to create something beyond the sum of two people.

AI excels at maintaining that local maximum. It can confidently reassure you better than any human can even if you're wrong. AI partners following this are successful now and people in their teens and early 20s are being hooked en masse.

Historically, superior pieces of technology haven't displaced older incumbents when the learning curve is too steep.

I don't see why a person dating an AI partner that has lovebombed them for several years would switch to another AI (or a person) that starts fights and bickers. Even if it's better in the long-term, that's still a marked decrease in short-term satisfaction.