I think explaining the reason to use it is another one of my reasons. Like I mentioned, it adds a step to a user's workflow.
It, however, is really useful for me and at work. I need to have strong passwords that are 10+ characters long but I can't write them down. So instead, I can remember something simple like the project name and use my app to generate the same password every time.
There are apps such as LastPass that pretty much solve the password management deal altogether, by choosing, storing and retrieving strong passwords.
IMHO, first of all, more thought needs to be put into the use case.
At any event, good luck and hope you'll find the path to succeed with your app(s).