When I learned guitar, the only 7th chord I knew was the dominant 7th. The blues-edged 7th chord. Not the mellow minor 7 or relaxing major 7. I still use it, but. "Dominant 7th chords have become rarer. The authors attribute the latter effect to the decline in the popularity of blues and jazz, which frequently use dominant 7th chords. However, we find that this effect holds widely, with dominant 7th chords diminishing in prevalence even when we exclude genres associated with blues and jazz. More qualitatively, musicologists have argued that many popular music styles in the 1970s exhibited a decline in the use of dominant 7th chords and a growth in the use of major 7th and minor 7th chords." Artemy Kolchinsky et al. Music follows fashions and trends. The reduced use of the 7th chord means it is out of style. If blues has less influence overall, it follows that there will be less use of the dominant 7 in other genres. Think of how blues-based 60s pop was. Now it's not. Think of how the Hendrix 7#9 came into prominence in the late 1960s. Chords have trends. The trend for the dominant 7th chord has diminished with time. Still, I am glad to know my dominant 7th in multiple voicings.