There's an explicit company policy about game development that is separate from their open source policy. It, among other things, prevents you from working on a game project with anyone else.
I always thought that they were doing it because they had a really low opinion of their own game studio. Maybe they were trying to kill as much future competition as they were able to (legally).
Their first (and only) title they seem to be pushing hard to the public (in my opinion, at least. The Grand Tour Game wasn't really marketed): https://www.newworld.com/en-us
Games development are limitless in scope and technical complexity and very passion driven. So, a developer could spend countless hours each night improving his game.
Next day, all the team has is a tired developer, drinking coffee and unable to code straight or analyse issues without missing subtleties.
Opening a wordpress for your mom and her gardening hobby is a significantly less time consuming task.
In the early days of Amazon, Bezos rejected bus passes for employees stating bus passes encourage people to leave work to a a timetable and he would prefer them to be at office and leave only when they can.