What would you use instead of ref counting? Swift is an embedded language for Apple’s own chips, they can optimize the hell out of refcounting at silicon level.
There really is only so much you can do - especially once you've got refcount churn on objects being used across multiple threads. Swift's refcounting can get truly annoying at times.
There was never any way to implement a modern GC while keeping compatibility with Objective-C, which was the primary design goal of Swift.
Apple had a bad experience with GC in ObjC with libauto and learned their lesson that C and GC just don’t mix. You can never have a truly modern GC in C, because C cannot provide any of the guarantees that a GC needs to move objects around.
Using a modern GC entails sealing the language off in a bubble. Since Swift is mostly used to interface with system frameworks, you would end up paying a cost when interfacing with the system frameworks written in ObjC, making your modern GC useless most of the time.
