>But even MPEG-1 supports a maximum resolution of 4095×4095, and a maximum bandwidth of 100 mbit. So it is technically possible to encode 4k (3840×2160) content even in MPEG-1, at decent quality.

The reality is that that despite MPEG-1 and MPEG-2 support those resolution, none of the mainstream implementation supports it. ( Although you could always use Software implementation as MPEG-2 is now patent free ) Hence when you go 4K, only newer version of MPEGs are used.

It is also missing MPEG-5 with EVC. And how not only MPEG-4 has different codec, AVC itself introduces many different profiles where compression efficiency differs greatly.