Very likely they might use some common frameworks that are shared between macOS, iOS, and watchOS to design (e.g. SwiftUI) and writing the whole stack for non-Apple platforms simply wouldn't make sense.

Understandable and quite possible, however that seems like a relatively lazy thing for Apple to do.

I'm not entirely sure what's the use case for most of these cards, but I'd hardly be surprised if this kind of decision didn't affect usability and accessibility for a lot of iPhone users, just because their venue guys don't have a mac.

And it's not like apple doesn't have the resources to make this software run across different types of computers. Iirc itunes and bonjour are (still?) very much developed by Apple for windows.