It might be useful for newbies (especially folks who don’t read the docs in this age of TL;DR) to have the buttons remind us of the shortcuts.
They are shown when hovering over the buttons (on the computer version).
But having to move hand from keyboard to mouse defeats the purpose of even having shortcut keys. The newbie I mentioned is just going to click a button without waiting for that to pop up. I’ve been using Anki for years, and have yet to see that.
I think it’s assumed that you’re going to memorize the shortcuts anyway, so you may not want them be sticking out all the time (which is distracting and takes space). I agree they are hard to find from the interface, but I don’t know of a better solution to convey them without making them distracting.
I believe anyway that anyone who needs the shortcuts and can’t find them in the interface can get them with a quick Google search. The shortcuts are documented and widely known and probably the most commonly used shortcuts (right after space bar/enter maybe).