Linux

That is a very good point. If the constraint was added that someone would need to purchase a new machine either way - their old one died lets say, and possibly they want to switch form factors from desktop to laptop or vice versa - then would it change your answer?

Trying to put Linux onto a new machine can involve literal horror stories, especially with a particular vendor of graphics cards (Nvidia) that seems to enjoy breaking things. And too many of the cool/special features that would "just work" on their machine if it were on an OS provided by the manufacturer - some neat-o keyboard buttons lets say - could take potentially hundreds of hours and ultimately writing your own driver coding to make it functional on Linux. Not always, obviously, but it can, whereas with a manufacturer-provided OS it is guaranteed to function right out of the box.

But yeah, getting a new Mac is something on the order of like $1000 USD, plus older machines have had more time for Linux drivers to have been written anyway, so cost and newness of the machine are definitely major factors.