As someone maintaining Obj-C libraries, I can see why. Usually the Swift examples are 90% the same thing so maintaining both is just a boilerplatey hassle. And really, I expect all competent iOS developers to be able to use an Objective-C API from Swift without even thinking about it, much less require specific examples.
With that said, I do find it useful to write unit tests in Swift, just to see that the Swift API looks as expected. So that’s one way to add examples.