To help combat streaming fraud, Spotify no longer pays royalties for songs that have fewer than 1,000 streams within a 12-month period.
If one of your tracks has earned fewer than 1,000 streams over the past 12 months, royalties will not be generated for that song. Note that this is on a per-song basis and not based on an artist's total stream count.
For full details, see Spotify’s official announcement here.
To learn more about promoting your music and increasing your streams, check out this article on the MusicDigi Blog.