The comparison with SELinux is a bit off, because SELinux is very different from RSBAC and other ACL-type mechanisms for limiting the attack surface of software

The comparison with SELinux is a bit off, because SELinux is very different from RSBAC and other ACL-type mechanisms for limiting the attack surface of software. SELinux is much more complex because it takes policy decisions like "this software is a Word Processor, it is not allowed to open files of the type Sensitive Document". That is very useful for those with that particular need, for others it is unnecessarily complex. A more common use case for regular users would rather be "run word processor without network access". That's where simpler systems shine. There used to be many access control mechanisms for Linux but they seemed to struggle to retain mindshare and remain a bit obscure. I would guess that's because so much is achieved by the old way of running software under their own uid and a chroot, so anything else already is a special case.