Spotify doesn't 'charge fees to artists', they charge fees to listeners and advertisers, to create a revenue pool, to pay out to artists.
And while that payout pool is roughly 70% of revenue, meaning they keep roughly 30%, the other point to be made there is that in the US the Copyright Royalties Board sets the repayment %'s, not Spotify, and they are increasing.
So pop songs usually have a recording artist / performer (i.e. the actually famous person whose name you know), and a songwriter/composer (the person behind the scenes who crafted the notes and lyrics). Sometimes they're the same person, sometimes there are many people credited for each. The takeaway here is that there are two separate pieces of intellectual property generated - the copyright (the songwriter's creation, the notes and lyrics), and the master (the actual recording of the song).
In the U.S., the money from a Spotify stream goes to whomever is the legal owner of the copyrighted work, just like FM radio. The owner of the recording master does not get paid.
When an artist signs a record deal, they usually give the label both the songwriting copyrights and ownership of the master, in exchange for some percentage of the profits generated by each. Super big name artists occasionally have the ability to throw around their weight and retain some ownership, but this is very much the exception rather than the norm.
