Valve removed it because it used official N64 APIs that Nintendo holds as classified information. I think if it had totally been bottom-up crafted from scratch, it would have survived. But Valve does NOT wanna deal with a Nintendo lawyer.
I think they’re referring to the fact that you can only continue using an unsupported version of MacOS for two years, not that the computer will only get two years of support.
Yeah Sega of Japan, particularly Sonic Team, actively refused to provide STI (American dev team) with source code necessary to build the game