"they chucked the entire operating system nine years ago"
It's not like they built another OS - NeXT had one ready to go - even ported to x86. IIRC, all previous attempts to write a new OS to succeed MacOS classic failed miserably.
What advantage NeXT brought is that it's a very modular OS. Unix programs, traditionally, don't look the OS from too close and that makes swapping file-systems easy. Or, at the very least, possible.
It's not like they built another OS - NeXT had one ready to go - even ported to x86. IIRC, all previous attempts to write a new OS to succeed MacOS classic failed miserably.
What advantage NeXT brought is that it's a very modular OS. Unix programs, traditionally, don't look the OS from too close and that makes swapping file-systems easy. Or, at the very least, possible.