I don't think loss leader is the correct term either.
YouTube doesn't make money, nor intends to make money in the near future[1]. The key here is to get entrenched in the market, then assert their monopoly.
On surface this might seem okay, but it definitely is anti-competitive. We've just gotten used to it. Dumping isn't the proper term, but was the closest I could find. It comes under predatory pricing, but the problem is, this business practice is so different from what the current literature consists of, I don't think there even is a proper term.
Uh, isn't that just abusing their monopoly position? It's not a problem that YouTube grows, it's a problem when they abuse their monopoly position. This is why we (United States of America) have antitrust laws.
"That doesn’t necessarily mean YouTube isn’t profitable, but it just means it’s not a focus at the moment. YouTube, which primarily makes money from advertising within its videos, doesn’t release revenue numbers (it is not separated in financial statements by parent company Alphabet). But some reports put revenue in the billions."
https://en.wikipedia.org/wiki/Loss_leader
Loose money to attract users/creators who put more money into the system.
I don't see how this would qualify as dumping in any way.