I think some of the reason for that is that enterprise usage of FreeBSD is frequently assumed to be via an intermediary, not directly as an actual FreeBSD insta

I think some of the reason for that is that enterprise usage of FreeBSD is frequently assumed to be via an intermediary, not directly as an actual FreeBSD install. RHEL directly supports enterprise installs, but FreeBSD is doing something more like producing a reference implementation. The enterprise installs that need N years of support lifecycle are supposed to run on a derived system (one of NetApp's, say), with its own EOL policies.