It's a combination between desktops needing a lot of dedicated space, and younger people not having such space, because they're children living with their paren

It's a combination between desktops needing a lot of dedicated space, and younger people not having such space, because they're children living with their parents. Naturally, the youth will gravitate toward devices designed for limited private space (laptops and phones), then when those kids grow up they continue using what they know.