Well, Debian Bullseye, a distro that hasn't even been released yet, already has a rustc that's so out of date (ie, ~5 months, 1.48) that it can't compile code written today using today's features. I guess if you come from the web or some "fast" internet company where you rebuild your entire world every day then 5-6 months is an eternity. But with, say, c++, I can expect to be able to compile C++ programs written by devs for a handful of years before C++?? issues start. And despite Bash 5 getting new features regularly I can expect a bash script written today to work on my 15 year old desktop running linux 2.6. It's not because these languages don't add new backwards incompatible features. It's because the devs don't immediately use them and say, "What is the problem with requiring a up-to date build chain?"
If you only talk to other bleeding edge devs in the rust community I can see how this ethos propagates. But not everyone is a bleeding edge rust dev. Some of us run our distros for many years and just want to compile programs.
Requiring the use of rust-up instead of using system repos is the often suggested way around this. But I, and many others, absolutely hate using third party compiler software from out of repos. It's a bad practice and leads to it's own trouble as shown the very topic this discussion thread is about.