OOP is at the very core of programming. You want to reuse as many elements as you can (reason applies) in order to save time, energy and make debugging and maintenance easy.
You can do it all manually. Imagine you place 14 text boxes and you’re not happy with the font. You now need to change it 14 times. If it was a user widget you’d need to do it once…
You can do it all manually, ofc, laboriously copy / paste stuff. But why?!