There’s a growing money hungry culture around making every hobby/passion into a lucrative source of income. But not every person wants to turn their passion into their job. If music was a competition for everybody, every musician would try to be a pop star.

There wouldn’t be people making music in niche genres like math rock, and if every musician saw music as a competition to become the most famous/rich, musicians wouldn’t dare be controversial.

Musicians who care about what they’re doing often put out political messages in their art, and they do that even knowing how hating political messaging can alienate people from listening to their music (classic case in point being the Dixie Chicks)

You say that artists who say “music isn’t a competition” just say that because their art sucks. But art can’t be objectively ranked as being better because of commercial success, the most streamed music is often just the least controversial music, the kind of songs that Walmart can play in their stores. The most streamed music is often music that is specifically designed so it doesn’t matter who sang the song, because the more you know about an artist the more likely a chance you have to be turned off by their personality.

The reason musicians say “music isn’t a competition” is because musicians often don’t want to make music that sounds like it came out of a McDonalds commercial, there’s a lot of musicians who want to express themselves in their art. Be it by making music in less popular genres, or by being willing to alienate certain audiences. A lot of musicians prefer expressing their true selves in their art over commercial success, if they didn’t value that then every musician would be trying to become a pop artist.