One CD sold at a gig for $10 is equal to about 2,000 Spotify plays. A t-shirt sale is double that. A mid-level band can play to 200 people a night and do $1000 daily in merch, easy (and I've personally done it). Sure, if people discover the band via Spotify, that brings them to shows, so there is the discoverability aspect - but the compensation is not remotely comparable.
Spotify profits off of the market value of streaming music having dropped to practically nothing (due to practically infinite supply), and their pay rates are terrible as a result.