It’s because most AC systems require forced air, so hydronic is a second system. You’ll find hydronics in expensive houses that can justify the double expense

It’s because most AC systems require forced air, so hydronic is a second system. You’ll find hydronics in expensive houses that can justify the double expense or in colder climates where the heating benefits are more important than AC. Also everyplace I’ve lived in the last 25 years has had detachable showerheads.