Note that redo is often ctrl+shift+z which is much easier to type. However redo is a weird case because traditionally most GUI applications (at least on Windows

Note that redo is often ctrl+shift+z which is much easier to type. However redo is a weird case because traditionally most GUI applications (at least on Windows) didn't have explicit redo even until late 90s/early 2000s and redo was just undo a second time (ie. undo was just a flip between the last and previous state). When applications started to add an undo stack and redo command there wasn't a commonly accepted shortcut key for it so they used whatever made sense for the developers - which is how ctrl+y (previous to letter z) and ctrl+shift+z (in Windows shift often inverts the action, e.g. alt+tab vs alt+shift+tab) came to be (though those weren't the only ones).