The thing is there are a number of people for whom they have never been just memories. There are people still using the original classic 68k machines on a day to day basis. And there's still stuff in there I miss in Linux. I don't use AmigaOS any more, but I do occasionally use (and even less occasionally contribute to) AROS, which is an AmigaOS compatible OS that runs on (amongst others) PC hardware either natively or under Linux.

As for memory protection, AmigaOS has a particular set of issues there: The OS is full of dependencies of message passing where the messages includes pointers, and where many apps may use the pointer passing to pass ownership of objects. Proper memory protection is incredibly hard to add to it.

With the resources of some large company, it might be possible, but to do it without losing a large percentage of the software catalogue, which is not being "replenished" very fast by ongoing development (though there are a few handfuls of commercial software products for AmigaOS still, and a small community of open source developers) would effectively require auditing of most applications to figure out how they're using the message passing, to try to find out how to avoid breaking them.