It only mattered the most because it was thought of last. If it was UX that increased impact by improving access, then it indeed mattered a great deal.
The article says " It turned out that about twenty years earlier IBM did sort of solve that problem with partition isolation, but they did that on custom mainframe hardware and architecture."
Right. I remember looking at technologies for virtualization on x86 chips before actual virtualization hardware existed on those chips, and they were pretty heavyweight, including rewriting the binary to replace privileged opcodes which would fail silently or behave differently in ring 3 compared to ring 0 with sequences of opcodes which would work to maintain the isolation. It was closer to emulation than virtualization given how much work the host needed to do to maintain the illusion that the guest OSes were running on bare hardware, and it really pointed up how the x86 architecture of the time just wasn't designed for that kind of thing.
For the past decade or so, mainframe-level virtualization on x86 has been possible, at least, starting on high-end chips and working its way downwards to the commodity world. And, yes, it exists in ARM as well.