This, btw, is also why someone else trying to replicate BG3 sales numbers won't work out for them, because BG3 was in a very unique position. Even those legions of D&D fans are not going to jump on to a future D&D videogame the way they did BG3, because they have now received their "good D&D videogame" fix. So another gane like BG3 won't move that needle much at all. I suspect Larian/Vincke understood this, and that was a big part of their decision to move on to something else entirely different. They have gotten all they can possibly get out of making that big D&D videogame the D&D fans have been pining after for years.
This is a fairly bold prediction! I'll make a totally different one.... If Larian makes another DnD game it will (again) break sales records before it is even released.
Basically, I do not buy the market saturation argument at all. Like it or not, Larian's game was extremely popular, and I wager that if a sequel were announced that it would be met with great popular acclaim.
Larian's decision to move away from BG for their next title probably has more to do with Vinke's quirkiness than anything else, but it may also relate to issues of dealing with Hasbro.