What this data shows is G Major truly is the "people's key." For those not familiar with music a 12 bar blues uses 3 chords: the so-called I, IV, and V chords (the first, fourth, and fifth chords in the key). In the key of G that would be G (I), C (IV), and D (V). Look at the most popular chords.
Instead of analyzing by chords I would have analyzed by key - what keys do you need? Convention says G Major is the "people's key" and so it makes sense to learn since so many songs use it. The key of A minor is pretty popular, and so is it's relative C major. Throw in E minor (which is G major's relative minor!) and with those 4 keys you can play the bulk of all rock and popular music written over the past 50 years!
Side note, from a usability perspective: G major is arguably the easiest key to play on a guitar, which is used heavily by both popular music and songwriters. The I/IV/V maps to G, C, D, which are all easy open chords to finger, plus Em is also simple (two fingers).
(Many of the other options include either B major or F major in the I/IV/V, and those are considerably more difficult to play)
Yeah agreed, G and E make the most sense for guitar for those reasons. Although equal temperament makes all scales sound the same in theory, there are often practical concerns. For example, EDM is very often in D#, E, F, F#, or G minor. There's a good reason for this: sub bass frequencies hit hardest around F. G#, A, A#, B and C sound too high, and anything lower than D# you risk playing on club speakers that can't produce the frequency well.
The key of G (G,C,D) is really easy to play on guitar and so is the key of C (C,F,G). A lot of beginning guitarists struggle with an F if you play it as a barre chord on the first fret of the low E string. My favorite option for playing an F is to play an FMaj7 using just the D (3), G (2), B (1) and e (open) strings which is an open chord. If you ask me to play an F chord that's what I'm going to play. I've also heard it referred to as the "rock 'n roll" F.
D major and A major are the other ubiquitous beginner-friendly keys for guitar. I distinctly remember a few months into getting my first guitar concluding that G major was so much better because Em is so much easier to play than Bm or F#m. :)
I've never heard it called "people's key" but a lot of rock and popular music written in the past 50 years was written on guitar where these keys are the easiest to play. I imagine Am/C are easiest on a piano but I am not a very good piano player to begin with.
The reason I approached this by chords instead of keys, is that I'm building an electronic instrument. [1] I can set it to play in any key before starting a song, but I'm trying to figure out how I should trigger chords (and what chords I will want to trigger) in the moment.
Instead of analyzing by chords I would have analyzed by key - what keys do you need? Convention says G Major is the "people's key" and so it makes sense to learn since so many songs use it. The key of A minor is pretty popular, and so is it's relative C major. Throw in E minor (which is G major's relative minor!) and with those 4 keys you can play the bulk of all rock and popular music written over the past 50 years!