Its worse then that because most of the users of cryptography aren't using it directly. It is often a layer or 3 down the dependency graphs. So its not unreasonable that the users weren't testing it.
There is a range of things the cryptography team could have done better.
1.) made it a major version change (i.e. 4.x) or even a new package name. This could be a bit extreme, but I would suggest if they are shifting to integrating more Rust, the package will likely have heavy internal changes.
2.) made a larger effort to understand how impactful the rust transition would be to non cryptography developers.
3.) Reached out to distro packagers to make sure they are aware. It appears they were focused more on PyPI users.
4.) Had a longer period of transition, Ideally with a public deprecation warning so that these users have had at least 6 months of logs they ignored before it broke.
However I think the blame needs to go to the packages that are using cryptography like ansible. They shouldn't have a floating dependency that allows a jump to a version that may be incompatible. Secondly the users of the package should be monitoring their upstream.
I think this is a larger issue under the surface for these alternative hardware platforms. Rust is becoming a major development language, and its side effects include much higher resource usage at compile time. I am not sure your going to be able to self host a Rust compiler on a m68k platform. This may be one of the points where a somewhat large portion of our computing hardware is "cut off", or alternative approaches will be required such as cross compilation. If Fedora, Debian, NetBSD and Gentoo wish to keep supporting these platforms it might require a considerable investment, however I wonder if it will be worth the time for most people.