The question is do they need all those tools and third-party addons to meaningfully compete with Unreal? Or is it enough to not have to pay the Unreal license fee? I don't know. Many (most?) AAA studios have their own game engine and they are not bothered by not having access to third party tools and addons. There are large AA studios that are still using CryEngine for new games, and I doubt there is a large ecosystem for that (although I don't actually know). At the same time, those studios have more money and employees to build those tools on their own. I imagine Valve also has a lot of internal tools that they could potentially release as well. Perhaps it's my own desire to see the industry converge on a high quality open source engine (which they can then heavily modify to their needs) that is blind-slighting me here.