Yeah, Valve has put a lot of effort into bridging the compatibility gap for Linux. Most of that work could also be ported to macOS, but they just don’t care.
It’s a shame, because getting 32-bit to 64-bit compatibility working would help Linux as well. I don’t know how much longer distros want to keep supporting 32-bit libraries, and some distros have already dropped them.
That said, macOS compatibility seems like a non-sequitur for an article calling Steam a “time bomb.” DRM is definitely the bigger issue here.