This works well in some ecosystems, but the C ecosystem has a "don't pessimize my weird implementation" goal. A bunch of different platforms wrap integers at different widths (or do different things entirely). Say you want to define it. Great! You probably pick the most common case. But now there is some weird embedded system that doesn't provide this wrapping behavior in hardware and the compiler needs to emit code to implement the wrapping and now all integer operations are slower on this target. These devs are now mad!

To get the "just define it all" approach you need people on weird ecosystems to be okay with paying for it. You think it is worth paying for (and I do too, frankly). But a significant portion of both the C and C++ communities don't - and that makes this very very hard.