So then you hug the right edge of the screen, looking for it, where it looks like it is, and where it's been for like the entire history of computing, and then you click, and there's just nothing there.
This is a special case of Fitts's law, where a button at the edge of a screen becomes effectively infinitely wide, as far as ease-of-clicking goes.
This was used intentionally with great effect on usability in the 90s and 2000s. (Scrollbar, start menu, show desktop, etc.)
In the last decade however the trend appears to have reversed: it is now fashionable be to make the scrollbar as difficult to click as possible, by offsetting it, making it narrower, or hiding it altogether.
