As you know, Spotify has several levels of access for the users, one of them is Freemium, for users with free accounts.
In these cases, Spotify does not collect money from users' subscriptions but from advertisers who pay to serve ads to these accounts. It is based on this money collected that it distributes the royalties for each reproduction that comes from a free user. This means that the price per stream in these cases can vary exaggeratedly from one month to another and even from one country to another.
The reality is that a couple of years ago, the price per stream of a free user has dropped severely. To give you an idea, if to generate 1€ with streams that come from Premium users an artist needs around 250 plays, to generate 1€ with streams from free accounts an artist would need almost 6,000 plays.