There are 3 possible reasons this is happening
This is a personal decision and there is no correct answer for every situation. We generally recommend you build up your site as an authority before enabling this.
We have done some testing on several of our sites to see which generates the most conversions. We have found that the default setting (requiring registration to see any properties) is the best.
You can have them both be the same or keep them different, whatever is most convenient for you.
Some google accounts do not have gmail capability. Your agent will have to link an account that does. Go here to see what all “products” you account has enabled: https://www.google.com/settings/products. Gmail has to be in there for that to work.
When people sign in with facebook, the only things we are getting from facebook are (1) their name and (2) their email.
We then ask for their phone number, which Facebook does not give us.
As a separate process, we use a third party service called FullContact which attempts to pull their social profiles in based on their name and email.
Depending on the users’s facebook privacy settings, we might be able to get their profile from FullContact, and we might not. Just because they used the facebook login button doesn’t mean that we automatically get their profile.