Wikipedia is using this site as the source, and that site shows around 20% market share for Mac. Linux is at 3% and ChromeOS is at 4%, so if you combine them and double that it still isn't at 75% of the market share Mac has.
This isn't mentioning that dealing with Linux compatibility is more annoying than Mac or Windows compatibility. Macs are very uniform, Windows has a giant making sure everything is compatible, and Linux has 900 distros that will never agree to co-operate.
The games are coming to Steam. Even if the launcher is there, Steam still gets the 30%