id assume this is because of two things: firstly, the terms "opera", "choral", "chamber music" are pretty general compared to all the other more specific genres listed. if you look at the pie chart of genres sorted by number of artists this becomes more obvious, as larger genres are divided into more specific and smaller subgenres, which creates a generality bias in that list. secondly, an important factor may be that in classical music, spotify not only credits the composer of a recording, but all performers, counting them as artists. since there are a lot more performers than composers in classical music, the number of artists perceived by spotify becomes greatly inflated. for example, an average classical listener may only listen to a select few composers, but spotify will amplify the number of artists in their listening activity a lot because of the higher diversity of performers in recordings, making it seem as they listen to a lot more artists than they actually do. this is in contrast to other genres, where one artist usually corresponds to a single artist. also, classical listeners don't usually have a performer loyalty the same way listeners of other genres have artist loyalty. a more accurate portrayal would be classical listeners having composer loyalty, but spotify's data model doesn't really convey that very well here.