You're talking about Bitcoin Gold, correct? I don't think Coinbase honored the Bitcoin Gold hard fork, they'v never announced that they were going to support it. Coinbase doesn't have a policy of supporing "forking coins" (umm, the forked coin in this case would be Bitcoin). Coinbase always, and by always I mean rarely, issues an announcement stating if they will support a forking coin.

Coinbase isn't in the business of supporting all these newly forking coins, so if that concerns you get your coins off of Coinbase!