An IPO provides 1) a fundraising opportunity 2) a liquidity event 3) an opportunity to fulfill contractual obligations
One of the conditions of their recent debt financing was that they IPO within a certain time frame. If they believe that they don't need additional funding at the moment or can get better terms then they are simply fulfilling criteria #2 and #3 with their unique IPO. I imagine Spotify can get decent debt financing terms b/c they have such a steady and predictable source of revenue (though not necessarily profit).