It's just a further example of the software / online experience being so...fluctuating as a whole. Which has its pros and cons. Pros being freedom of visual and interactive expression. Cons being lack of expectation.

My router doesn't accept a username at all, which actually makes a bit of sense since there's only one 'account' on it. Unfortunately, this means that neither the browser nor LastPass will save the password. My previous router allowed me to change both the username and the password, then pre-populated the username field with whatever I'd entered (but didn't disable the field), which I always thought was odd...

In that case, I just click the icon for my pw manager (1Password in this case), and the modal shows me the same message.

Some places require no additional info from you.

There are good use cases where third party logins are good enough.