Because prices differ between exchange quite a bit, and Coinbase is considered one of the more legitimate ones.
Because it's only worth what people are willing to pay, and that's how much Coinbase are paying at the moment.
Well there are more people that are willing to pay than just Coinbase. A more comprehensive answer would be that arbitrage is not that up to speed in the Bitcoin world, especially in KRW and JPY markets:
https://coinmarketcap.com/currencies/bitcoin/#markets
Used to be that crypto is massively overpriced there, now it looks like Korea and Japan are leading this price fall.
> A more comprehensive answer would be that arbitrage is not that up to speed in the Bitcoin world...
Or that folks trust their ability to get money out of Coinbase more than the other exchanges.
I assume Coinbase prices come from GDAX. Anyone know for sure?
Yes, every time you buy or sell on Coinbase it’s transacted through their GDAX platform.