As a jazz musician I’d estimate that there are at least an order of magnitude more seventh chords than triads in jazz songs. I question a dataset that says there are more triads. Makes me wonder what else is wrong with the data.

For instance, G being the most common key in jazz doesn’t ring true. I’d wager that it’s Bb, Eb, F in some order.

Maybe all of the songs in this set were simplified for guitar players?