APIs designed for and built in Objective-C have been the mainstay of Apple application development ever since the Cocoa framework, stretching all the way back to NeXTSTEP in the 1980s. Even with the advent of Swift, most of today's iOS and macOS APIs carry the legacy of Objective-C. Much of development with Swift has involved with attempting to use the new language for old APIs. Perhaps legacy alone does not make it good, but it certainly demonstrates that there has not been a need to rewrite all of it using newer languages, that Objective-C has been reliable and venerable.