It’s a nonsense argument to say Google can’t handle credential stuffing without SMS 2FA in place, as in not pushing all 2FA via Google Authenticator and using the very wide reach and talented security team for baseline cred stuffing. Sec tools for this, even without being Google and their very talented sec team, are pretty good.
Wanting a hard phone number is a pure identification play and also about the more likely pragmatic concern (than cred stuffing) of using Google for burner accounts.