Chromium is open source doesn't ship with the proprietary, closed bits of Chrome, like the EME DRM module which is used here. So this is Chrome-only.

Open-source software can obviously never properly support DRM.

Which is why Mozilla/Firefox was so much against this whole HTML5 DRM bullshit in the first place, and so should you have been to.

Yes. Only chrome includes the Widevine binary blob and supporting source code in the browser.