What's the biggest challenge with Music streaming?

So a few years ago I was working with one guy from MMO that was making xxx,xxx from music streaming on Spotify. I was designing song picture designs at that time for him and he was paying me way too good. He stopped after a few months and he did tell me it doesn't work anymore (he probably found better cheaper designer but anyways)..

From what I saw online there are still many people doing this.

I was wondering, what is the biggest challenge with this model?

Geting people who will listen streams probably. (if You don't doing any blackhat things)

was he legit as an artist? Or was he using playlists etc. to earn streams?

I am streaming on liqusic.com, works great, always got my payouts

Can you share your method? I never head of that website