For sites/apps that can't fetch the password themselves, people usually copy paste the password. This could allow other sites/apps that have access to the clipboard to see the password.

Why would you ever let a site or an unstrusted application access your clipboard?

I think you're more protected in the browser. On iOS any app can access the clipboard without having to ask for any permission.

The encryption scheme on iOS is nice, but for how much of a game they talk about privacy Apple had the opportunity to do so much more for security around identity/auth and they did approximately nothing.

Because you usually don't have control over that. On lots of system, any application that can display an UI can access the current clipboard's contents.

Taking a step back from the problem, users do usually have some amount of control over what is running on a system.

I mean, I understand that computers managed by typical users will be a shitshow, but much of the problem in that situation is that they don't really care.

Is there any way to globally disable clipboard access in my browser? Jeez, this sounds horrifying!

I believe the browser is one of the few applications that already take this into account, fortunately. Clipboard access from Javascript is secure, for example.

Another good reason to use iCloud Keychain rather than one of the 3rd party ones.