One might think of this as an attempt to avoid drawn-out licensing negotiations with the labels, as Spotify already has licences in place. But the deals that the labels have in place with Spotify (of course, their negotiations are covered by non-disclosure agreements), would most likely have clauses that would require re-negotiations when a third party is involved. It's been suggested that Spotify is seeking up-front guarantees from Virgin Media, in the same way major labels would have done when making a deal with Spotify.