Valve buys up dev teams that are about to shake the industry up. Valve haven't actually been the ones to make something new in a long time. TFC, CS, Portal, DoD, L4D, Alien Swarm, Dota 2... were all made by outside dev teams that Valve absorbed and put their name on. The only things Valve have actually made, themselves, in the last 5 years are Alyx and CS2, neither of which brought anything new to the industry (although they are wonderfully-executed games) and are both sequels of existing franchises.
Personally, I'm not a fan of this practice, because I feel like Valve inadvertently stifles these studios after they bring them onboard. For instance, the team from DigiPen that Valve bought for their Portal tech? Imagine if they were still able to make games. Imagine if they were still able to stretch their creativity and create new tech and ideas. Instead, their intellectual properties are all tied up at Valve and they got to release two whole games in the last 20 years. Who knows what we could be missing out on from these guys if they were able to actually still make stuff.
No, but they exist at the whim of Bluesky. Having multiple endpoints on your network doesn't make it decentralized, if every endpoint is controlled by a single entity. This is an important distinction, because Bluesky can prevent a specific instance from interacting with the entire ATProto network, something which is not possible on ActivityPub, as there is no such authority who can completely shut down anybody else's instance.