Short answer: noone bothered to implement something like this. /bin/strip
was developed when memory was a precious resource and it increased the challenge of debugging.
My best guess why:
In ObjectiveC (and swift) functions are called by objects sending messages to each other in a kind of dynamic dispatch.
That means when you call a method on an object, you send identifiers of the object you want to call the method on and the method itself to the dispatch function (e.g. objc_msgsend). My best guess is that stripping symbols complicates that process.
References: https://blog.zynamics.com/2010/04/27/objective-c-reversing-i/