- Their previous game Divinity: Original Sin 2 was critically acclaimed, very popular for a pretty hardcore CRPG, and had long legs.
- DnD has a lot of brand power and has been strongly in the zeitgeist for years.
- There's a big cohort of millennials who have strong nostalgia for Baldur's Gate and who have plenty of money to buy games (if not time to play them).
- The Early Access release for this game was wildly popular beyond the developer's expectations, and maintained interest for years.
I definitely underestimated the brand power of DnD and Baldur's Gate because they aren't very important to me, personally. But also there have been a load of really good CRPGs in recent years and there seemed to be a pretty low ceiling to how much interest they could get. Tyranny, Pillars of Eternity, Pathfinder: Kingmaker, and a few others were amazing and beloved CRPG games but were lucky to have a tenth of the success of BG3. But those games were generally less accessible, mostly not multiplayer, and again lacked the brand power.
I feel slightly offended being thrown into the same pot as those weird millenials ;)
Absolutely everybody who owned a PC for gaming in the late 90's played BG1 and BG2, no matter the age. Video games are not just for teenagers you know.