Because the need for higher-level, easy to use environment is served well by middleware, the so-called "game engines", Unity and Unreal.
There's intermediate level APIs, like the old OpenGL 4 and DirectX 11, or slightly more modern portable alternatives like bgfx and sokol; on the web, there's three.js.
The subject field is complex, the applications are also primarily complex, so there's not much value in something that lets you "easily" drop a few cubes on an endless plain (like the VRML of old days). There's no 3D equivalent of "I'll make myself the web site for my barbershop" that started the Web 20 years ago. (or, to be more pedantic, "the page for my high-energy physics experiment" 30 years ago.) Nowadays even the Web is hellishly complicated. Maybe if VR/AR takes off (any moment now), there will be need for "simple 3D", but I suspect it will be handled by custom "easy" versions of Unity/Unreal rather than people writing to a "simpler 3D API". The way people aren't making barbershop sites in "simple HTML", but going to Squarespace.
There's intermediate level APIs, like the old OpenGL 4 and DirectX 11, or slightly more modern portable alternatives like bgfx and sokol; on the web, there's three.js.
The subject field is complex, the applications are also primarily complex, so there's not much value in something that lets you "easily" drop a few cubes on an endless plain (like the VRML of old days). There's no 3D equivalent of "I'll make myself the web site for my barbershop" that started the Web 20 years ago. (or, to be more pedantic, "the page for my high-energy physics experiment" 30 years ago.) Nowadays even the Web is hellishly complicated. Maybe if VR/AR takes off (any moment now), there will be need for "simple 3D", but I suspect it will be handled by custom "easy" versions of Unity/Unreal rather than people writing to a "simpler 3D API". The way people aren't making barbershop sites in "simple HTML", but going to Squarespace.