Soundcloud is predominantly used by electronic artists who have never been much into big labels, instead preferring small independent labels or self releasing.
Artists in other genres and styles I find tend to use Bandcamp.
At the end of the day though, if an artist takes off, they're going to have to find someone to invest in them for advertising, marketing and pressing their vinyls / cds. Because none of that is cheap and you can only get so far by yourself.