This seem like a huge leap in sales, but it needs to be taken with some context there also.
It surely is a great success and any game can hope to get those numbers, but BG2 was also huge.
1st, population was 2 billion less in 2000.
2nd, amount of people with PCs and internet connection in 2000 vs 2023.
3rd, shift in culture about "nerd" culture in last 10 or so years.
it's easier to create hype today than in 2000 and not to mention Steam and seasonal sales on it, yes there was no big discount on BG3, but it was some, and that also works on buying psyche.
The increase in population is about 35% over 25 years.
Global PC sales have about doubled over the same 25 years.
And the shift in 'nerd' culture has been going on for a LOT longer then a decade.
The highest number in there is just double the PC sales in a quarter century, while the difference between BG2 and BG3 is a LOT larger. In the first two years BG2 did 1.5 million sales, even if the market doubled that would be only 3 million, not the 20 million BG3 did.
In 2011 Skyrim was released. It also 20 million sales (that's more then the decade of nerd change you mentioned ago). After 12 years they sold 60 million copies. Starfield (2023, by the same maker), in the last two years did worse then Skyrim from almost a decade and a half ago. There's a reason why they only mention players and not actual sales figures, as the game was on Game Pass and everyone and their mom
tried it. It's like counting the amount of demos downloaded as sales figures. Starfield is also 18+, but it isn't as well received as BG3. Making something 18+ doesn't guarantee success, it just opens up a whole field of potential players that
could purchase it. Minecraft on the other hand has sold something like 350 million copies and is only 7+ in Europe... Sidenote: Diablo II (2000) sold 4 million copies in it's first year.
We can of course compare all kinds of games, but the reality is, before the massive sales of BG3, D&D was always a small niche. BG3 was essentially a mass market game with a D&D label. It succeeded not because of the D&D label, but despite of the D&D label, it was received as a VERY good game.