Why? Why do we have to accept it?
You don’t have to, but I’m sure Disney would like other people to.
Why would it divide the fandom further?
Because there are people out there who actually like the sequels (believe it or not), and Disney suddenly saying “that never happened lol” would majorly piss them off. That’s exactly what happened with TFA going out of its way to shit on the prequels, and I doubt Disney wants to repeat that mistake.
What is wrong with dividing the fandom?
Disney wants money. Fans give Disney money. If Disney pisses fans off, they stop giving Disney money. I could not make this more simple.
Why is it better to salvage something?
Because then the people who still like at least a bit of the sequels will become much more pleased with the franchise as a whole, and the people who unconditionally love the sequels will just be pleased to have that story expanded on. Again, when this strategy was applied to the prequels via the Clone Wars show, it was received much more positively than “just pretend it didn’t happen” was for TFA.
Why is it possible to salvage anything?
Again, it may not be possible for you, but there are plenty of people out there who see at least a few redeeming qualities in the sequels’ story. If Disney can expound on those mostly-liked elements, while rationalizing the bits that pissed fans off, I think the sequels can be redeemed in the fandom’s eyes.
Why are they “the main saga?”
Because Disney branded them as such, and contradicting your own branding is almost never a good idea.
In a nutshell, it feels like you’re seeing this from a subjective, opinion-based point of view, while a corporation like Disney will go with what’s most economically sound. And from what I see, attempting to redeem the sequel trilogy is the most economically sound direction to take the franchise. No matter how you feel about the sequels, they will always be part of Disney’s canon.