It says (pretty explicitly, if you go back and read interviews), that Gabe Newell really doesn’t like Microsoft in general, that the feeling is mutual and that the fact that his multibillion dollar empire is stuck as a Windows application MS may try to muscle out at any point has motivated him to bring PC gaming out of Windows from very early on.
Granted, MS has been sucking at attempting exactly that for a long time, but that’s the ultimate motivation here. That’s not a particularly disputed fact.
“Forced exclusivity is bad” is an angle that has always baffled me a little, because some of its proponents seem to also be going “what exclusives does the Xbox have” like two posts down the road.
Or maybe it’s because I’m old enough to remember where the “I will never buy anything on Epic because they pay for exclusives” was instead “Square has betrayed its customers by moving to the PlayStation” (or, you know, Konami for having Xbox ports).
Gaming opinions are weird, and get weirder if you track them over time.