Re: Because ... it’ll just work : Nope
But actually, they really don't. Because Apple will just stop your machine upgrading to the latest O/S. And then block you updating to the app store with the old O/S. And various other "need the latest OS" to run software.
My daughter just got rid of a 10 year old single core Vaio. That also worked. And was running Windows 10 And upgrading to SSD was easy.