Ah, the truth is sinking in as the wisdom from so many answers combines.
The big challenge for the independent stream programmer is making people know you are out there. And you have hundreds -- no, make that thousands -- of competing streams which you are essentially lost somewhere in the middle of. Marketing is indeed not cheap; as
@KilowattKat said, SEO isn't cheap, and with so many other streams out there, even marketing can't make you
the choice for your target listeners.
It's no surprise that the lion's share of streaming comes from the major players, who can both aggregate various genres into a single app and promote, promote, promote. It's even more so for podcasts; if you listen to
any podcast at iHeart, for example, I can guarantee that at least two of the commercial inserts promote other podcasts. Even if you could convince other streamers to include spots for your stream, you simply don't have the strength of numbers behind you.
And what
@TheBigA posted while I was writing this is correct, not just from the question of advertiser interest but the question of someone finding you in the first place. Any independent stream is akin to the proverbial needle in a haystack.
And now we get to the part that most people who want to attract an audience for their stream will hate the most: Your niche programming, consisting of songs that are your personal favorites that "no one else plays" is not going to get you a loyal, returning audience. You're going to have to adopt a lot of the same programming techniques as terrestrial radio does. We get return listeners by consistently playing the songs that have been shown to be consensus favorites. Stray too far from that and there's always going to be other streams for the listener to switch to.
What BigA said about a global audience is right on the money, but that means you have to be as mass appeal as AM/FM is. Even SiriusXM's "niche" channels are heavy on the familiar favorites; you don't hear them play one low charting song after another.
Yes, you can do the local version of global, as
@MrCrumpets suggests, and his advice for doing that rings true with me as a programmer. But you are still going to have to be "all things to all people" in terms of music, and I suspect that goes against the philosophy of those who want to start streams in the first place.
Get the programming right in terms of holding the audience once they find you, do whatever marketing you can afford, and then resist the temptation to get too creative.
But don't think the world is just waiting for someone to play them the B-side of the lowest charting hit by the Dave Clark Five. They're not. You have the same challenge as the rest of us, and that is creating something listeners will come back to over and over again.