Earlier quoted context omitted.
I remember those days too. They had nothing to do with computers not being behind a NAT.
They had to do with computers being directly addressable, routable, and reachable by the entire Internet, which was the default prior to widespread deployment of NAT. NAT isn't the best way to do it, but it probably is the single biggest factor in reducing the external reachability of endpoint IPs.
It's a shame the likes of Microsoft only care about "zero trust" insofar their compliance checkboxes with the the US government. They see it as a chore. Contrary to Google, Cloudflare, et al.