The alternate explanation is that it's rather pointless to integrate it because all new Macs are ARM, and there are basically zero Windows games compiled for ARM.
Not likely considering Valve are working on an ARM version of proton in the open, have published test results for x86-64 windows games playing on proton-arm64ec-4, and there are credible leaks that the Steam Frame uses an ARM cpu.
If anything Valve is moving towards ARM and taking the library along with it.
If anything Valve is moving towards ARM and taking the library along with it.