AFAIK Apple’s “services” revenue is a little over a quarter of their total; everything else is hardware, dominated by the iPhone. Mac hardware is <10% of total revenue.

iPhones are largely locked to their App Store so no risk there. Macs (currently) aren’t locked to the App Store - and I’d guess that Mac App Store usage is middling as a result.

Which is to say, I doubt that a marginal Mac App Store revenue hit from a small proportion of users switching to Linux over MacOS is the driver for not supporting Linux development. I’d guess it’s more about an inflexible company culture and maybe not wanting to extend their area of responsibility and risk.