I'm honestly not really sure how it went down. It's possible that XNU (the macOS kernel) was simply developed before FreeBSD Jails were developed, and they never put in the engineering effort to port over the feature. I don't think there's a fundamental reason why it wouldn't work.

For devs, I think that most devs are okay with the current practice of running a virtualized Linux (or other) guest via Docker and deploying to Linux (or other) servers. macOS does support virtualization. The difference between virtualization and containerization is that a virtualized guest uses its own kernel whereas a containerized guest shares the host kernel.

I'll also point you to two comments in this old HN thread which seem to have good information about Apple's use of server operating systems:

The possibility of Jails in XNU: https://news.ycombinator.com/item?id=31384534

Apple's use of Linux in the Services division: https://news.ycombinator.com/item?id=31383746