SELinux is pretty inflexible and incompatible with multi-user systems that deploy stuff without privileges - it assumes you can have global policy that applies

SELinux is pretty inflexible and incompatible with multi-user systems that deploy stuff without privileges - it assumes you can have global policy that applies to everything, which doesn't work well with containers, or browsers, or even just running things out of your home directory. Hence, kernel devs would like to increase adoption of something that's a little better designed - not SELinux.