Because they are paid to, or rather because those who curate popular Spotify playlists are paid to. See also https://en.wikipedia.org/wiki/Payola
The Wikipedia article you linked does not back what you're saying..
The “also” implies relatedness. It is a broader trend in the music industry. For a specific example with Spotify, you might recall the Drake promo debacle from 2018; where “Scorpion” was so thoroughly pushed on to users that refunds for Spotify Premium were demanded on the grounds that the degree of promotion crossed a threshold into outright advertising, which premium was to be free of.
Payola is illegal now, and it's funny that you even bring it up in this context because there was a time when payola was one of the only ways that independent labels could actually get music on air. It circumvented the overlords. The "respected" institutions didn't want to go near rock.