The millions of deployed systems have people who don't need to touch the SELinux configuration. The people who are dissatisfied with SELinux are those who use it until they have to install something that requires they change the policy; then they look at the hundreds of thousands of lines of policy and say 'life is too short'.
This is even true in areas such as massive stockbroking servers, where they really do care a good bit about security. Not even there do they care enough to make SELinux work with them: what in a simpler system might be a small possibility that a config fixup might break something, in a system of the complexity of shipped SELinux policies becomes a *large* possibility in these people's eyes. So they always turn SELinux off. And I think they're right.
Probably nowhere outside the military would people care enough to fix such problems. Of course, that's where SELinux emerged from: and it's probably a good fit for there.
If we want a security framework we can configure ourselves without driving ourselves insane -- if we occasionally have demands not met by our distributors -- then something simpler, something *comprehensible* is needed.