Browsers don't save the TOTP seed and auto fill it for you for one, making it much less user friendly than a password in practice.
The main problem I have with MFA is that it gets used too frequently for things that don't need that much protection, which from my perspective is basically anything other than making a transfer or trade in my bank/brokerage. Just user-hostile requiring of manual action, including finding my phone that I don't always keep on me.
It's also often used as a way to justify collecting a phone number, which I wouldn't even have if not for MFA.
(I have written a TOTP implementation myself. I do not have a GH account, and likely never will.)