Pardon my ignorance, but what is the incentive driving artists to work with these record labels rather than self-publishing? Is it not possible to "self-publish" to Spotify and Apple Music without a record label? Is it strictly to increase exposure in the way mentioned in this paragraph, i.e. to have their music included in various mixes/albums from different labels?
Finally, what is the barrier to starting a record label that anyone would want anything to do with? I would (in my ignorance) think that an artist would have more leverage here, since they already belong to the community