This is more just something I'm curious about than something I want an actual answer to. I recently started learning Premiere Pro CC 2019 (installed on a Windows 10 machine), and was struck with something about the couple of Adobe products I use that I never really noticed before, and don't really understand. Premiere, Photoshop, and Illustrator all use Alt as the key to zoom in and out with the mouse wheel.
Every other program I can think of uses Ctrl for mouse wheel zoom. Everything from GIMP, to Inkscape, to web browsers like Chrome and Firefox, the entire Office suite, and Windows Explorer all use Ctrl + Mouse wheel to zoom. And this works really well. It's quick, intuitive, and consistent across multiple platforms. But for a reason I can't really fathom, every Adobe product I'm familiar with uses Alt.
Normally this wouldn't be a big deal, there are other hotkeys that are inconsistent from one program to the next and you can learn to adjust if you're bouncing between a couple. But this specific combination of Alt + mouse wheel has been really inconvenient to use for zooming in and out of the timeline in Premiere. For as long as I can remember, Windows has used the Alt key as the operator for the menu bar hotkeys. Alt + F for the File menu, Alt + E for the Edit menu, etc. This operator also functions as a toggle, so you don't have to hit Alt and the F key at the same time to open the File menu, you can press and release Alt and that will switch the application's focus to the menu bar to anticipate hotkey presses.
This makes Alt a really troublesome key to use for mouse wheel zooming, because Windows doesn't recognize the scrolling of the mouse wheel as a key press. This means that when you press Alt in Premiere, Windows switches the application's focus to the menu bar to await a hotkey, but doesn't always recognize that you only needed it for zooming in or out of the timeline. This means that the menu bar hotkeys remain active after you're done zooming and release the Alt key, intending to return to normal use in Premiere. But if you then, for example, hit the C key to switch to the Cut tool, Premiere instead opens the Clip menu, and awaits another hotkey to open a Clip menu item. You then have to either press Alt or Escape to return to normal use. This also disables mouse wheel scrolling while the focus is on the menu bar, so if you zoom in to find a particular spot in a clip, and then try to release alt and use the scroll wheel to navigate through the clip chronologically, nothing will happen.
The other problem is that this is inconsistent. I haven't been able to figure out why, but it seems that sometimes when you release Alt, Premiere does return to normal use, as I'm sure is intended. But other times, the application's focus stays on the menu bar and overrides all the normal Premiere hotkeys. It doesn't seem to matter where the cursor is when you initially press alt, or where you release it, or if you started with the timeline active or a different panel active. I just can't tell what affects it.
If it consistently switched focus to the menu bar every time, I'd eventually learn to just hit Alt a second time after I'm done zooming. And yes, once you learn to watch for this behavior, you do get used to having to check whether or not the items on the menu bar are highlighted and hit Alt again to get back to normal use, but this feels VERY clumsy. And from what I've been able to research, there doesn't appear to be any way to remap this key to Ctrl in Premiere itself. I see a lot of suggestions for third party applications to accomplish this same functionality, but I'm not comfortable using most third party applications (especially to accomplish something that feels like it could be done natively). I've also seen people suggesting to press Ctrl + Alt and then using the mouse wheel to zoom, which does work, but this seems silly when it would be much simpler to make it just Ctrl instead.
I don't understand why Adobe products don't use Ctrl for mouse wheel zoom like the other applications I'm familiar with. Is there a reason it was designed this way that I'm not thinking of? Is this the key that's used for mouse wheel zooming on another OS and they want to keep it consistent across multiple platforms? Do most adobe customers use multiple operating systems? Why can't we remap this key press? Ctrl + mouse wheel does scroll vertically on the timeline if you have multiple video or audio tracks and they can't all fit in the timeline panel, so I know that key combination is technically being used by another function. However, Shift + mouse wheel doesn't appear to be used for anything on the timeline. Why can't Ctrl + mouse wheel be used for zooming, and Shift + mouse wheel be used for vertical scrolling? Has this never been an issue for any Adobe customers who use Windows? Am I doing something wrong??