I suspect an overwhelming number of those who find BG2 the apex of RPGs are roughly 32-38 years of age (born between 82-88), based on a premise (which certainly could be wrong) that our formative years (roughly 10-16) are the most impactful. Most (by a large margin I suspect) born after 88 probably never even played BG1&2, with there being so many more 'modern' alternatives like EverQuest. Most (by a large margin I suspect) born before 82 had plenty of previous games to fill the sacred slot of 'best game ever' (e.g. table top D&D). So, if the range of possible gamers who might play BG is (say) 10 to 70, that 7 year range of 32-38 are a small minority. I could certainly be off by these figures a bit, but I see no reason to suspect that many gamers younger than 32 or older than 38 hold BG1&2 so high. Hence, the niche.
Those are quite a lot assumptions.
Admittedly. But, I do give what I think are legitimate grounds for those assumptions. To put it differently, with the explosion of 3D rpgs around 1999, I suspect many rpg fans born after 88 wouldn't even give a game like BG the time of day; it very quickly looked archaic compared to the likes of Everquest. On the other side, by the time BG was released, those born before 82 likely had the pedestal reserved for something else (most likely D&D itself). BG just couldn't rival the substance of what came before it (D&D) nor the technology that quickly came after it (FF7, Everquest, Zelda Ocarina, Ultima 9).
Once again, if Wizards of the coast had wanted BG3 to look and feel like BG1&2, they would have hired Obsidian and not Larian Studios. Which tells a lot on what their expectations are for the game.
True, we shall see how they like it now when it looks like DOS1 and 2.