It's inconvenient. That's the primary reason why it won't gain mass adoption since any obstacle to your service will lower the registration / engagement metrics.
With password managers built into all modern browsers, casual users (which, lets be honest here, are by far the most of the web users) do not have to worry about typing passwords. Security be damned. If it is not invisible to the user, they will reject it.
With password managers built into all modern browsers, casual users (which, lets be honest here, are by far the most of the web users) do not have to worry about typing passwords. Security be damned. If it is not invisible to the user, they will reject it.