It doesn't look like it has many (any?) strings. Aside from being split over three years in Blender's case.
It is worth considering that this is in Epic's best interests as Blender + Unreal Engine is a common platform for startups/indie devs.
Making Blender better may make the games that people develop using Unreal Engine better, which might mean higher license income for Epic. So it is a win for Epic and a win for Blender/the community.
End users get new features they may actually use, massive OSS gets funding. Win-win for all parties.