I'm not buying a phone with 512GB-1TB of storage just for my music, 5G is available everywhere and my home internet connection is plenty fast. I can just stream it from home - maybe sync some locally if I'm going off grid.
And moving files manually one by one to my phone? Oof. It's not the early 2000s, we have better solutions.
If a 512GB phone costs you $300 dollar more tahn the one you would have bought, it amounts to $2 per month for a 5-year phone. Spotify is three times that.
And as a bonus everyone in my family can listen to the same collection without having to upgrade to a 1TB phone. And I can use the same source in my car, on my laptop, desktop etc. All without having to waste 400GB of space for music storage on every device.