When you’re making a new phone, you’re still making a phone. There are hundreds of constraints already present. Ditto for a car, or an app to help you manage your money, or a pair of running shoes. Innovation suddenly feels like an ever-narrowing alley, with little room to move.
It’s thus pretty easy to see why copying happens - because when you see a mature product that’s somehow managed to innovate (to be “new” whilst balancing all the constraints and annoyances of the existing problem), it becomes almost impossible to see how you could do it any other way. Design blindness sets in: the most successful product is the only possible design. Which, of course, is nonsense - but a very convincing, insistent, tempting sort of nonsense.