Re: Who for?
A not entirely uncommon use case for Linux on Macs is for Mac users who find their current Mac eventually stops being supported by MacOS updates (boo), but still is perfectly usable hardware. The Mac can then be repurposed for another use with Linux, or passed on as a hand-me-down. Consigning older but still functional computers to recycling is still relatively wasteful if further use could still be made of it otherwise.
The Mac user will still most likely buy a new replacement Mac when necessary anyway, so it's not as if Apple are losing out. Apple would certainly get quite a bit of goodwill by not putting obstacles in the way of running Linux (or *BSD) on Mac hardware.