I don't really understand how this benefits Spotify as it doesn't improve the service in any way that I can see, and such a move likely makes it worse for users for petty business reasons that have nothing to do with the users.
In the short term, the only negative impact would be if the songs they're demoting are extremely popular and if the public perceives their absence as a loss in quality. Given the size of the musical corpus these days, that seems unlikely.
In the long term, this serves notice to content creators that there's no such thing as a free lunch. Normally, those content creators would have to balance the cost of exclusivity (fewer plays on those exclusive songs) against the benefits (presumably dramatically improved promotion and possibly higher royalty per click. With this policy in place, those content creators have to factor in the loss of the vast majority of their income from the other providers—not just on new content, but also on old content. That significantly changes the balance in a way that discourages these exclusive deals.
And that's a good thing. Vendor exclusivity is inherently anti-consumer.