It would need a benevolent, and very wealthy, collection of artists or sympathetic patrons to fund growth, or it would simply be out-gunned by the rest of the industry that actively works against artist independence.
One of my businesses is a worker-owned cooperative. It has challenges that are completely novel to me (having started two small traditional corporations before that), and they're very difficult to overcome. Herding cats is hard, operating under the cooperative principles is hard(er than doing it all for profit), and raising money is effectively impossible for many types of cooperative, as far as I can tell.
Building a competing music or video service to YouTube and Spotify would require tremendous resources, and without the big cash-out promised by those ventures, I don't know how one would make it work.
I'd love to be wrong. But, I've been an indie and DIY and punk music fan almost my entire life, and I've worked in the music industry. It's better than it's ever been for independent artists in many regards, but Google and Apple aren't on the side of artists all that much more than the historic record industry was/is, and it's very hard to have them as an adversary. Would you want to try to compete directly with Google or Apple? And, if you were someone with tens of millions of disposable income would you want to risk it on a venture that is likely to fail and if it succeeds won't do much more than pay back your investment capital and a small bit of interest?
The parallels are stunning in this case. Thank you for mentioning your perspective, as I think it bears repeating that the "music industry" has always been like this - the names and methods may look different, but the model is the same. Ain't nobody signed to iTunes or YouTube, near as I can tell...
It's a nightmare, though. It is ruled by the bureaucrats running it, in conjunction with the artists that actually profit from it, i. e. old people with a large back catalogue. It's constantly fighting with the businesses using music, i. e. youtube still blocks 90% of videos with music because they haven't agreed on prices. Clubs might have to close because they've tripled prices recently. Small bands sometimes sign up, only to find out they actually have to pay to play their own songs, and through the magic of the most convoluted payout formula ever, might not actually get as much back as they pay in. Even if they get something out of it, it may take 18 months.
Even if they didn't build and run the platform themselves directly (due to the fact that a bunch of artists have better things to do) - if they contracted out the development and maintenance to a third-party company - they'd have ownership over the platform, be able to switch maintenance company, and therefore take their fanbases with them if things start going wrong.
It's not as infeasible as you might think; artists' cooperatives, as a business structure, have a long history, and creating a digital space is, in many respects, more cost-effective than a brick-and-mortar location.