I don’t think this is true in the long run, they’re just not a priority when things like ABI stability and a concurrency model are still in progress. There has been some skepticism expressed about how important HKT and the usual FP abstractions are. My sense is that HKT is pretty likely as a language feature someday but we’re unlikely to see even Functor added to the standard library without pretty strong motivation demonstrating concrete problems it solves in Swift.
There is a thread on the topic that had a lot of activity recently you may wish to read: Higher Kinded Types (Monads, Functors, etc.)
If you haven’t seen my gist showing how to encode HKT in Swift today you may also be interested in that: Emulating HKT in Swift · GitHub.