Let's assume 2GB of data. That is roughly 500 songs, ~2000 minutes, roughly 2 days if you stream new tracks non-stop at 16 hours a day. So that's roughly about 1GB per day.
So 1GB a day, 30GB a month. The most expensive carrier in my country offers 50GB data quota a month for ~$7.50 USD. Even taking to the extreme scenario, looks like it's still fairly affordable.
In reality, the app will cache songs that are already streamed so any repeat plays won't incur more data. And most people don't stream non-stop every day. Furthermore, streaming services like Spotify and Apple Music allows pre-download of songs/playlists so they can be played offline.
People spend more data watching TikTok/Youtube. Music streaming is actually affordable nowadays.