In the businesses that I've worked for we always took rational decisions based on the numbers, feedback from customers, our capacities, deals, etc. If you know those things, the vast majority of business decisions that companies take are really quite understandable.

There are several reasons they might have taken this decision, one might be that it was part of a deal they made with Facebook. Spotify is probably aware that like most websites, they are a fad, and they need a way to survive. They've chosen to become a cleaner fish for a much larger animal that will provide them with food and protection, in return for a valuable service. It's neither a good, nor a bad business decision. It's a rational one.