It's not up to the people to replace UIKit with SwiftUI, it's up to Apple. Swift was able to replace Objective-C very quickly because it offered everything you needed. (Well, except for interoperability with (Obj-)C++).

SwiftUI, however, is still very reliant on UIKit beneath its surface. And if you want to use anything more exotic than buttons or lists or images in your app, you will quickly have to turn to Appkit/UIKit to fill your needs.

And the reason is simple: Both UIKit and SwiftUI rely on CoreGraphics and CoreAnimations to render their components. The difference between the two is UIKit gives you access to the underlying system - ultimately giving you complete control to a very low level, whereas SwiftUI doesn't. (Not yet, at least.)

Until SwiftUI delivers the same control and power UIKit currently delivers - just like Swift did compared to Objective-C - we're still gonna have to rely on UIKit quite a bit!

Hopefully it's before 2029 ;)