Based on some customers feedback, they usually don't participate in our site because they feel like forced to register on userecho.com (the same actually happened to me the first time, it took me some guessing till I found I can actually use 3rd party login).
It is because of the way the form is presented, with the focus on the text box and the other options at the top but don't getting users attention.
So since it is easier and gives more confidence to users, I think you should redesign the signin popup. See image below.
I am sure this will increment users participation across all userecho.com project sites.