Do you have any other work in your portfolio -- perhaps showing some frontend work? Github is a little bare. We're an early-stage startup looking for a frontend dev to built out our prototype.
The reason they want a portfolio is because they'll be investing time and resources into you and while you may be confident in your ability to deliver, they're probably not.
If you end up failing to deliver, it would be wasted time and resources on their part. The point of a portfolio is to show that you have the skills to do what they're looking for.
Don't let the other guys drag you down - they sound bitter. But from their perspective, you're not giving them anything to work with. Fill the gap pronto! :)