It became a kitchen sink language similarly to C++. For all the hate Java gets, they did tackle language development very well - wait a bit for other, niche languages to be your testing ground of new features, and only add what sticks. Swift literally has all the features you can find in today’s modern languages, and they have some inconsistent interactions with each other. Also, even this litany of features isn’t enough to make SwiftUI implementable only as a Swift library, it uses some specifics not available in the language otherwise.
And also, as most apple dev tools, it is the only modern language whose compiler failed under me (other than being slow as hell) - I have never gotten a type inference timed out error in other languages, even though it has been around for a time :D
As for growing a language, this is a must watch (bear with the presenter for the bit, you will soon understand why he talks strangely in the beginning): https://m.youtube.com/watch?v=_ahvzDzKdB0