Is DRM required for streaming services you describe to exist?
Is DRM required for streaming music? Definitely not.
Is DRM required to make money out of streaming music? Debatable.
Putting it on a comparable service, look at GOG.com and Steam. They are both digital game distributor services. Before GOG.com people thought DRM was the only way to make a viable business out of selling digital copies of videogames, as presented by Valve. Then GOG came along and they said "nope, we hate DRM, we're gonna sell digital games without it". Now, is their system viable? Well they've been around for quite a while, I don't know if their money comes directly from game sales or other sources (their parent company also owns CDProjekt which makes Triple A games like The Witcher) but they are still in the business after all these years.
You can't look at the GOG.com on its own because its unclear if the non-DRM "benefits" of a site of GOG.com are being subsidized by Steam.
If Steam was vaporized tomorrow, would GOG.com be profitable enough to support the salaries of not just GOG.com, but the developers, producers, designers, and QA testers of the game studios? If not, it's not viable. Is it? I'm not sure because Steam is the main bread winner.
Is that enough to support main game publishers and developers? I have no idea but that's not the point I was trying to make. The point I'm making is that it's obviously profitable for the people working at GOG.
Why does it matter if Steam disappears? Do you think people would just stop buying games altogether without Steam? People use Steam because of the platform it provides, not because of the DRM. If people wanted to just pirate games they could get the GOG version off a torrent site since that is already DRM-free, it's not like Steam's DRM is stopping anybody from distributing pirated copies.
Technically? No, it isn't required. But it seems pretty necessary if you want to have deals with major labels and publishers. There already exists a musical equivalent of GOG. Bandcamp [0]. Music sales are DRM free, you can choose your file format and quality, and you can stream any artist DRM-free on the website or app. However, you won't find the latest Taylor Swift or Kanye release for sale on Bandcamp or anywhere without DRM.
Most of the point of the DRM for Spotify and Netflix is just so you don't sign up for a week and download the parts of the catalog you like and then quit. That's why spotify uses DRM and itunes doesn't.