I suspect they also hope developer choice gets reframed from "Unity or Unreal" to "Godot or Unreal." In other words: Unity gets bumped out of the picture since Godot can do what it does and is open source, while Unreal stays comfortably in the hyperrealism/high-end perch.

Unity is Unreal Engine's biggest competitor by far. Godot competes with Unity (mostly for 2D games) but is at least a decade off being any threat to Unreal.

So yes, funding Godot is A Nice Thing To Do but it also conveniently puts a bit of pressure on Unity, their biggest competitor, without impacting their own business.

Also, if you believe Matthew Ball's take[0] then Epic is all-in on fostering as many gamedev-ish creators as it can so that it can loop them all into making content for its metaverse later. As you alluded to, in the long term funding a FOSS game engine which is focused on ease of use helps that too.

[0]: https://www.matthewball.co/all/epicgamesprimermaster

It expands their empire like Microsoft pledging to "support" Open Source: it's disingenuous, self-serving, and develops a "claim" of authority over the sector. It allows them, the makers of Unreal Engine, to develop a business relationship with their competition and influence the trajectory on one of only major alternatives in order to control the market more.

If Epic Games really cared about Godot, they would align more with their values in-house. Their M&A drives the organization like a propeller.