2011 was a different time in terms of starting channels, I think. Plenty of the ones they provided funding for [1] didn’t really turn into anything, but a few ended up being very big deals (Crash Course sticks out the most to me)
Nice find digging up that list, which makes it seem like 80%+ of those promoted channels didn't succeed. And if you exclude the "mainstream media" channels (e.g. Reuters, Slate, The Onion, etc.) which had an existing audience prior to YouTube, then the success rate is even lower. This does make Numberphile seem like an outlier even amongst the promoted channels.
[1] https://web.archive.org/web/20120210205023/https://www.youtu...