[kbenson]

Yes, that's where I would suggest putting it, but the reason projects don't is either because they aren't aware of it, feel it's a bit more convoluted to make sure you update where PATH is set, or that /opt is generally used for singular applications, not an extended hierarchy such as /opt/local (which is actually a truly weird name, /opt/macports/ with /opt/macports/bin, /opt/macports/lib, etc would make more sense). It makes sense to use /opt from an "application" point of view, but I think the problem is many of these package managers see themselves as more than that, and as pseudo-system components, which clouds their reasoning.

The LFS spec you linked to is actually ancient at version 0.65, the latest is 3.0 and available here[1]. It's a bit "do what you want", but it really expects the "local" part of /opt/local that MacPorts uses to be some sort of identifier for MacPorts.

That said, it's the Linux Filesystem Hierarchy, so it only applies to Apple stuff inasmuch as it's common practices for UNIXes in general. And it's not like the major Linux distros follow it fully either. They're happy to break from it where it preserves some historical layout their OS has had that they think is easier for their users/admins.

1: https://refspecs.linuxfoundation.org/FHS_3.0/fhs/index.html