When it was available for Windows, nobody used it, except web developers who wanted their website to work on Macs, but didn't have a Mac to test with.
These days with hidpi screens the difference between font rendering between windows and Mac is negligible though. So that's not a factor anymore.
Where you're getting these numbers from? Doesn't sound right to me, but maybe I just have a biased sample. I'd guesstimate that 50% if not more of my friends with macOS run Chrome, small percentage (2 or 3) runs Firefox and the rest Safari.
Most people I know with Macs have at least two browsers installed, but then most people with Macs I know are fairly tech savvy.
I mean, that's a huge draw in the consumer space for mac/ios. Remember the scale were at here. Something like 250,000,000 ios devices a YEAR.
As an example, Safari is the only choice if you don’t want to give more marketshare to Chromium but also need to programatically control or retrieve information from your browser. Firefox has no AppleScript support, which disqualifies it immediately.
Once other browsers are allowed on iOS, it's possible more users will migrate on both desktop & mobile to Chrome/FF.