GitHub becomes much more comfortable with the Refined GitHub extension. It adds a bunch of keyboard shortcuts, among a ton of other small improvements.
I think nothing prevents a web app from having keyboard shortcuts, but more often than not what I see is web apps having bad keyboard shortcuts that hijack the browser's natural behavior (taking over <ctrl>-f is a good example). I think often people go at this as if it's an Electron app and not a browser that has literally a hundred other interfaces loaded into it, leading the user to have certain expectations.
All that aside your Gmail example is spot on, and I'm one of those google-hatin' dudes.
Notice how I can list with `gh pr list` but then will need to run a full new command to actually inspect the contents of those PRs. I think an interactive interface would be nice!