one issue as site owner is why would I use your service and not just stick with Facebook login. Facebook give me access to everything I need. I have no reason

one issue as site owner is why would I use your service and not just stick with Facebook login. Facebook give me access to everything I need. I have no reason to go with your service. If and only if you got some huge traction would I need to implement your service, but your whole idea is based off the idea that people want to use your service to login/authenticate to my site.