It was a couple years ago, but I spoke with one of their engineering managers about Swift adoption within the company. His response was that it was being used for new apps/projects, but not so much for existing codebases.

Having worked on a large Obj-C codebase that began adopting Swift, there are definitely some headaches involved in Obj-C/Swift interop, and you often aren't getting many benefits of Swift unless your new code has few to no dependencies on / is not depended on by Obj-C code, unless you can refactor it into Swift.

Given how quickly it seems they've been forced to ship, I can understand not wanting to deal with these issues, or not having the time to address them.