Spotify and its direct competitors pay nearly nothing for streams. There is very, very little money coming in from that for most artists. And if it's on streaming, why buy it?

Certainly there's benefit to being easily listened-to, in terms of promoting other revenue streams (live performance, mostly, but also potentially licensing or merch or whatever). And you don't get paid NOTHING for Spotify streams. It's just that one $5 or $10 Bandcamp sale is thousands and thousands and thousands of Spotify streams.

So they're trying to maximize their income.