My guess would be a monetary justification. After all you can't just have developers working on year old laptops and devices when you can make them buy new ones by making this one simple change.
The reason is platform coherence and control, and lock-step updates. To avoid cases like this:
https://segmentfault.com/a/1190000040213084/en
https://ntdotdev.wordpress.com/2021/02/06/state-of-the-windo...
...and not the insignificant money that could be made from devs updating a laptop a little earlier (especially since you can trivially use a still supported 5-6 year old laptop anyway with the newest Apple OS, and you wouldn't see any major performance issue, except in cases like the Intel to ARM switching. So what would they gain? Developers forced not to use an 8 or 10 year old laptop? As if they would?).