I think Jails started as a tool of it's time, it's about the same thing as virtualization in making isolated systems when dependencies start to diverge, but aimed at the issues of sysadmins that had to manage their own systems, not a quick developer experience.

Even if "jailsfiles" were created the ecosystem would need to start from scratch and sometimes it feels like people in the FreeBSD ecosystem have a hard enough time keeping ports somewhat up to date, let alone create something new.

Luckily Podman seems to support FreeBSD these days for docker images, but the Linux emualation might be a bit of a blocker so not a 100% solution.