iOS has historically done a lot better with less RAM (as far as how snappy and responsive it feels) than Android. Dunno if that's still the case, but it very much was for years and years.
Unfortunately this can be hardly retrofitted to other OSs since it requires cooperation from the apps.
Now if you want general ref counting you have to use atomic counters, and those will trash your performance on modern machines beyond fixing. And then we didn’t even mention that big object graphs will have to be recursively freed, an overhead that can’t be amortized in this case. Oh and you do need a tracing step one way or another to free cycles.