Android phones are build on managed code, but PC computers are built on C/C++ mostly (almost all productivity apps, browsers, games, the operating system itself). And the only GC code most people run is garbage collected on apple too - it's Java Script on the web.

I'm not familiar with MacOs, are the apps there mostly managed code? Even if they were and even if refcounting on Mac is that much faster than refounting on PC - refcounted code would still lose to manual memory management on average.