>>538653> I'm not too sure why software devs can't agree on a convention (maybe continuity issues within the same software? idk)
It's not necessarily even consistent within a particular software package. E.g. 3DS Max was notorious for using different coordinate systems for different subsystems (they may have fixed it by now; I haven't touched it in over a decade).
has a point. If Z isn't up, it's because someone was too focused on the screen, treating 3D purely as "graphics", just like 2D but with an extra axis bolted on.
For physics, and for modelling environments (rather than objects), you have a horizontal plane and a vertical axis. That much is a law of nature, not a human construct.
And if the horizontal plane is X-Z, then either the developer got too far in before they started actually thinking about anything, or (if the horizontal plane being X-Z was intentional) they need their head examined.