why is BB so popular?

[Carrera]

It hasn't. BB had coherent visual presentation, models that were on average higher quality than 2021 games and worked together to maintain immersion all while having good environments of same quality.
The gameplay systems were grindy but provided the required gameplay challenge to elevate the experience, although this aged poorly.
It defined what good incest scenarios should be and had archetypal incest relationships that were copied widely.
eg. little sister with the mind of a 12y old who is taught sex, bitchy older sister than acts as antagonist and is brought down, mom with the body of a 20-something who starts off having power over you but loses it, male antagonist who is trying to have a normal relationship with a woman of his age who is defeated by the womans evil rapist son and so on.

And that is your opinion just like my post was my opinion, and based on the many replies in this thread as well. Yet you're trying so hard to speak with some sort of authority on the subject.

I stand by mine, about the only thing not surpassed by pretty much everything is is the renders, still pretty epic. The story is contrived, the actions/consequences are utterly and completely predictable (even for when it was new).