If PVC-U had been available to builders in the past, they would have used it. No one disputes the beauty of timber, but it has drawbacks. In the wet, it can swell. In dry conditions, it can shrink. It can warp or twist and whatever else you do, you’ll always have to find the time to take good care of it.
Imagine never having to paint a window. Imagine never having a window already welded shut with layers of paint. PVC-U windows are tough, durable and insulating. They need hardly any maintenance. They open easily and when they’re closed, they are secure.