ASLR isn't actually good security mechanism. It's been effortlessly bypassed by Windows malware since XP, so why do we care so much about implementing it on new systems when the attackers have very good methodologies to defeat it already? It adds a lot of complexity to the kernel that will be hard to revert in the future when it's properly solved in hardware (CHERI).

The only reason FreeBSD is implementing their limited version is because there are some LLVM features I can't recall the name of that can produce some pretty hardened binaries but it requires some ASLR-ish kernel support