That is the usual mentality in FOSS circles, the 3D APIs are a tiny portion of what makes a game engine when placed the set of bullet point of what something like Unreal must be able to deliver to a team, while targeting all these backends,

"Windows PC, PlayStation 5, PlayStation 4, Xbox Series X, Xbox Series S, Xbox One, Nintendo Switch, macOS, iOS, Android, ARKit, ARCore, OpenXR, SteamVR, Oculus, Linux, and SteamDeck."

https://www.unrealengine.com/en-US/unreal-engine-5

> That is the usual mentality in FOSS circles

I don't know what this means.

> "Windows PC, PlayStation 5, PlayStation 4, Xbox Series X, Xbox Series S, Xbox One, Nintendo Switch, macOS, iOS, Android, ARKit, ARCore, OpenXR, SteamVR, Oculus, Linux, and SteamDeck."

Yes, I understand backends. Why isn't a new target for graphics that supports some of those backends at least some of that effort reduced?

Because writing a plugin for a 3D API is quite basic effort in the grand scheme of what a game engine must provide.

Scenegraph, assets management, scripting, fonts, 3D models, shader debugging, a myriad of visualisation algorithms, sound,game devices integration, networking, GUI framework, artists tooling, game designers tooling,...

Note that Unreal supports Linux, and even so, very few studios using Unreal bother to sell to Linux users.