Bioware and CD Projekt worked together on the first Witcher, because that game ran on Bioware's engine. The new director for Phantom Liberty and Cyberpunk's sequel came from Bioware, and he said in an interview that that past relationship is why they reached out to him for the position, insinuating it's not the first time it's happened and that the two companies had continued to be in contact over the years. Given CD Projekt's last two games' similarities to Bethesda's formula, it wouldn't surprise me if there was overlap with the developers of those studios as well; and the same extends to Larian and the inspirations they've clearly taken from old Bioware.

as far as I know Troika just disappeared along with it’s developers

It's possible that all but about 5 developers from Troika left the industry after the company folded, but I'd call that the least likely scenario. In my own career (only briefly in games), people who liked working with me have reached out to hire me from previous working relationships between companies, and you tend to see a lot of the same people from job to job as a result.