This obviously can't be trivially gleaned from those statistics - but would you say most of the bishop/rook promotions are just showboating, or are they done to avoid stalemates?
I, of course, understand why people would promote to a knight.
I'm an 1850 player and when I am playing under extreme time pressure (e.g. < 2 seconds remaining), I occasionally underpromote to a rook because I can execute a rook+king endgame mechanically faster than a queen+king without an accidental misclick causing a stalemate.
That's interesting. Is it just easier because you can't accidentally move to diagonals, or it's easier in your mind because you've seen it more? If you can even tell the difference.
Not OP but with rook and king you make a box and shrink it while keeping your king next to your rook, and stalemate is all but impossible. With queen and rook you have to get the queen to a knight's distance from your opponents king and mirror their moves until the edge of the board, and at the end you need a slightly bigger L (4 squares) to avoid stalemate while your bring your king around. In the former the two pieces work together, in the latter they work somewhat independently (with a quirk at the end) until the final sequence of moves and therefore there is a slightly larger risk of error. In practice you should drill this regularly to mitigate the risk.
>or it's easier in your mind because you've seen it more
I think the point OP is making is that if you need to use your mind at all with <2 seconds left you're going to lose. Pre moving safe legal moves without hitting a stalemate is definitely easier without a queen.
A rook promotion is something regular chess players will need to do to prevent stalemate, but it isn't that common where it is required (as opposed to someone who could win with a queen instead but it is trickery so beginners should go for a rook ). A Knight is the better promotion choice often enough that you should study tactics that lead to it, while a rook it is enough to do a stalemate check before promoting. There are tactics that only a bishop wins, but they are things you study for fun, not because you expect them.
Ahh you're right; I should have thought of that possibility! It turns out my data is more or less garbage; mea culpa.
In fact: all of the =R promotions I inspected were frivolous, and 4/5 of the =N promotions were frivolous. I'm surprised it's that bad. One scenario where this happens is "capture-promote, followed by immediate re-capture".
I, of course, understand why people would promote to a knight.