They probably should have thought longer about the success of Baldur's Gate 3 before burning their bridge with Larian.
It wasn't their IP that made it succeed, it was the quality of the developer. D&D as a brand is worthless if they just sell it to the highest bidder and don't give a damn about quality.
On the bright side I would much rather see a Divinity Original Sin 3 than a Baldur's Gate 4 from Larian. Now they are free to do their own thing again.
Tbf Divinity: Original Sin 2 did not come anywhere near BG3 levels of popularity. The difference between those can really only be attributed to the value of brand recognition.
The fact that they think it's part of the same strategy is why they fail. They take a cursory look at both, see numbers go up, and think that all they have to do is push for common element X to succeed.
Gross oversimplification of business strategy and how products are built are why corporations trip over their own dicks over and over again. I wish they would just teach that in business school.