What we really need is 'scrollbar-width: thick-ol-windows-95-bar'
Why do designers hate scroll bars :-(
That's why designers don't like it. It's just an unbalanced use of pixels. It's visual clutter.
Unfortunately, none of the alternatives are great, either. The thin ones are hard to use when you do want them. Making them appear and disappear is distracting. Some applications make use of the space (letters in a long alphabetical list suggesting where to scroll, error indicators in an editor), but it's nonstandard and not always applicable.
So designers keep looking for better alternatives. Ideally, you do away with scrolling, but that's not always feasible.
Is there really a shortage of screen space? Scroll bars were introduced on like 14" monitors with a 640x480 resolution. Wasn't a problem then. Why is it we're running out of pixels on a 42" 4K monitor?
I just don't understand why interfaces must be invisible. If anything, a scroll bar provides contextual clues as to what sort of an interface you are looking at. It's something that can be scrolled. It also lets you know where it begins and ends, neither pieces of information are rarely obvious with contemporary GUIs.
Don't underestimate the power of design conventions in making an interface intuitive.
Another fun thing: On Mac OS you can enable scrollbars to always show; but doing this adds a ~18px scroll gutter on every scrollable element, and thus breaks some scrolling web elements where the designers clearly only designed around the default. :)
The scroll wheel is so sluggish and the cursor keys are a lot slower still.
Also I'm not an apple user.
The bar seems to be more familiarity and less functionality to me.
To scroll through a document the size of this thread, I need to paw at the scroll wheel 10 times. It's at the same time slow and imprecise. With the scroll bar, it's a single gesture, it's quick and immediate with pixel precision.
Neither paging, search or expanding/collapsing elements permit this level of control. They're all much slower, and to make matters worse, often implementation defined.
Scroll bars always work the same in every window and every application. Overshooting the mark is a non-issue because scrolling is so fast correction is trivial and immediate.
The alternatives also have a big problem with focus-ambiguity. If I page-down in the text box I'm typing this into, it will page the text input, and not the document. Using the scroll bar to adjust the view, there is no such ambiguity, since the mouse cursor uniquely identifies which element I want to scroll.