A pop musician is not an artist and someone who keeps a journal is not an artist (usually).
Although seemingly on opposite ends of the public-private spectrum, pop musicians and private writers are not artists for a similar reason. They are not actively engaging with social and political ideas, neither are hoping to arouse change or action in a larger population. While exceptions always exist, and while pop musicians are reaching a large audience, I would claim that the majority of pop music today is simply entertainment as opposed to art, thus making them entertainers instead of artists. Similarly, anyone who writes, or paints, or draws, or even plays music in the comfort of their home, or behind closed doors, is not an artist. They are a writer, painter, illustrator or animator, or a musician, or a user of whatever medium they choose, but that does not make them an artist. Every square is a rectangle, not every rectangle is a square; every artist is a user of a medium, not every user is an artist.
John Cage was an artist because he took risks in cultural, social, and political spheres.
Having recently read John Gallaher’s In A Landscape, I cannot help but point to the man who inspired Gallaher in multiple ways, John Cage. Two examples are his composition 4’33” (https://www.youtube.com/watch?v=JTEFKFiXSx4) and his question posed to world leaders (cited in Gallaher’s poem): “Why do we kill people?”
I don’t mean to discourage anyone from expressing themselves creatively because I am in full support of all forms of expression, they are meaningful for the development of self and even for relationships. However, there is a reason we question the responsibilities of an artist; they have responsibilities in their interactions with society.