Especially the big stores like Spotify, Apple Music or Amazon often report much lower sales than expected. This is usually because expectations were too high. Please keep in mind that 60,000 songs are released on these platforms every day. Many others disappear in the service's database and can only be found through a specific research. If you or your interpret are still unknown, hardly anyone will look for your song or buy it. Unknown artists can only become famous thanks to their own qualities and to self-promotion.