How come square can't use the built in NFC reader?

I have a card reader installed on my android phone. Works great.
Why can’t square use the built in NFC reader to accept payments instead of having to use a Bluetooth device that you have to carry around?

At this time the ability to take payments with the built in NFC reader on Android devices isn’t currently available. You’ll need to use the Square reader to connect via bluetooth to complete payments. :slightly_smiling_face: