That's because it's impossible to implement that functionality in iOS with its locked-down APIs. It's the same reason that Microsoft's Your Phone app is limited on iOS compared to Android. On iOS, only Apple has the privilege to implement such features and they limit the interoperability with macOS.
Considering that your're not allowed to do anything interesting with the system when developing for ios, that's not surprising to me. I connect my android with my gnu/linux machine and my windows videogame box, that's all I tested.
I did see some Reddit thread about someone creating an iOS port but saying that it lacked all the functionality of the Android app.