They could certainly "clearly pass the cost" of this on to the user by not offering Audiobooks to users who didn't pay for the "+ # of Audiobooks" tier of Spotify Premium; instead of this horrible enshittified crap where it cuts you off midsentence like a greedy telecomm provider would. Or perhaps their limitation should be on how many titles you can listen to concurrently in a certain time period. (So if you open X books; that's it; you have to shelve one or wait it out)
It certainly means that Spotify did a bad job at negotiating their rights to these audiobooks as well. That matters too; because that makes the product worse; and that should never have been allowed to happen. If they couldn't have offered it nicely, they could've just not offered it at all or added it to a higher service tier so that the cost is diverted better.