It’s 2 extra button clicks to generate a password and save it on 1Password, and you never have to leave your current context.

Versus for email OTP you have to switch to your email client, find the email, perhaps refresh a few times waiting for it to come in, click into the email once you see it, highlight the OTP, click copy, then switch back to the app and finally paste. I don’t understand how anybody could possibly prefer it.