That’s a fairly narrow assumption of the environments where Blender is actually used:
- Blender might not be a game engine, but it is used quite a lot for creating 3D content for game engines to produce games, VR/AR applications or even educational tools. Some of these game engines use Z up (e.g. Unreal Engine).
- Blender is used in architectural visualization, interacting with “industry standard” tools that use Z up (e.g. Rhino3D).
- Blender is used in science for creating and processing scientific models, some of which use Z up.
- Etc, etc.
Apart from the Z-up versus Y-up discussion there’s also the left-handed versus right-handed coordinate system discussion (e.g. Unity uses a left-handed coordinate system, while Blender uses a right-handed system). All in all, there’s 4 variants (nicely summarized in a picture already shown in this thread I believe) and those are here to stay for the foreseeable future.
Yes, it’s a pain having to deal with conversion from one of the variants to another when you are forced to, but what would be much worse in my opinion is to make it configurable in Blender to specify what axis needs to be up. This would split all Blender models/files into two camps that are hard to use together (e.g. appending or linking a Y-up file to a Z-up scene would either imply converting the appended data or having the user change the orientation manually to match). You will end up with the same challenges that there are currently when interacting between different software packages, but then within the Blender community. It will also lead to other shared resources, such as tutorials, to get split into two variants, which doesn’t help those learning.
Blender is (thankfully) not only used for CGI. Yes, many of its concepts (materials, rigs, meshes, lights) are aimed at CGI-like workloads, but they are general enough to be usable for other tasks. Plus it’s extensibility through Python is a real strength, allowing it to be used for work different from producing CGI. I would go so far as venturing that Blender would not have become the big success it now is if it hadn’t been picked up outside of CGI and 3D animation. The adoption in all kinds of environments is precisely what made it’s foothold grow stronger over the years as it was the go-to open-source package if you needed a flexible 3D application regardless of the field you were working in.
It would help if the Blender imports and exporters would become more mature and more aligned. E.g. add control over axis mapping to all of them and not just a subset as is currently the case (STL, FBX, …). This would make a lot of the current challenges in dealing with files and external applications using a different coordinate convention easier. Heck, you could even let people add their own import/export preferences in how to treat certain types of files.