I'd say it's both. More viewers, so per-view revenue is down, but more creators and videos as well so per-video revenue is also down due to increased competition. The net result is what you see today on channels - ad revenue used to be plenty for creators, but now they're plugging sponsors, merch, Patreon, and anything else they can to make up the shortfall.
True, but that's a separate issue from the one being discussed in this article. Increased competition between creators may make it more difficult to get viewers, but it doesn't directly hurt CPM.
