Apple purposely make it so after 3 new versions of the OS you cannot upgrade the OS on the hardware any further. This in turn means you cannot install new software as the applications themselves require the newer versions of the OS. It has been this way on apple hardware for decades, and has laid the foundation of not ever needing to provide backwards compatibility for more than a few years as well as forcing new hardware purchases. The 'emulation story' only needs to work for a couple of generations, then it itself can be sunsetted and is not expected to be backwards compatible with newer OSes. It is also the reason it is pretty much impossible to upgrade CPUs in Apple machines.
> IMO, this is better then carrying around 40 years of cruft.
Backwards compatibility is such a strong point, it is why windows survives even though it has become a bloated ad riddled mess. You can argue which is better, but that seriously depends on your requirements. If you have a business application coded 30 years ago on x86 that no developer in your company understands any more, then backwards compatibility is king. On the other end of the spectrum if you are happy to be purchasing new software subscriptions constantly and having bleeding edge hardware is a must for you, then backwards compatibility probably isnt required.