Many laptops also have touch screens. I'm not saying it's the only way... I'll also note that over-crowding a UI also leads to poorer quality UX in the end. P

Many laptops also have touch screens. I'm not saying it's the only way... I'll also note that over-crowding a UI also leads to poorer quality UX in the end. People find more than a handful of options on the screen or in a given area at a time difficult to manage, at least initially. It will vary of course, some technically advanced users will often prefer a more dense ui/ux. Also, scaling a UX as you suggest takes a LOT of additional up front design consideration and effort (roughly 3x the effort every time you add a single target variance). My own experience on the developer side, is that you rarely have good design or UX guidelines as it stands in most projects, let alone appropriately defining and testing how you transition or show more than one UX. For example, how many times have you seen a website that's different for phone or desktop, and one side or the other are missing functionality completely, meaning you often have to force-switch leading to a poorer experience overall.