Wider and wider monitors that are higher and higher resolution, so the bottom left gets farther and smaller from the eyes. Nevermind multi-monitor setups.
>Being a fan of the "classic" labeled taskbar, taskbar items with text could provide a lot more info
Text requires translation/localization, which is extra work, which is extra cost. Pick a generic, ideally universal icon and it's once-and-done. Also, not everyone can or will read.
>the elongated click area is larger and more predictable.
While I agree, ultimately most people are going to find working with a mouse to be complicated and arduous because it's simply not a "natural, human" action.
>presenting just icons means there has to be a second level grouping if the same app has multiple windows.
You can have multiple buttons with the same icon, you know. A good example of this being the taskbar from Windows 10 and prior with window groupings disabled.
>Touch displays? Should be irrelevant in desktop mode.
The unfortunate reality is the desktop form factor has become a second-class citizen, best we (as in us nerds and graybeards and wizards) get used to it because that reality doesn't care for our chagrin.
>High DPI screens that demand dense rectangular items? The tradeoff seems to be big to be just that.
If anything, higher resolution screens demand circular things because they obviously look smoother than on lower resolution screens.