MacOS does support subpixel rendering, has at least since the early to mid 2000s. One or two versions back though they turned it off by default since it isn't necessary on HiDPI "Retina" displays and they only ship HiDPI displays now.
You can still turn it on although it requires the command line.
Subpixel rendering dramatically slows down rendering text. When you have a high res screen, and want everything to be 120fps, even text rendering starts to be a bottleneck.
That combined with the fairly massive software complexity of subpixel rendering is probably why mac dropped it.
You can still turn it on although it requires the command line.