I am a bit shocked by how popular this game is. All the signs were there, though. - 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…
Also the studio was already known for quality and some of their own brands were already quite successful, making them more or less the top CRPG developer that also brought a lot of innovation to the genre. Although Baldurs Gate certainly is a brand that draws additional people. I could imagine that their other games will also get in the focus again when people are finished with the new title.
That said, all the games you mentioned were a success I believe. Maybe not that large, but I think they all were "surprisingly" successful compared to many AAA titles that wished they were.