Which other coins? Coinbase doesn't support many types of coins (only BTC, ETH, LTC), so I'm not surprised they are ignoring smaller coins. I just assumed they were not worth the hassle?

Ironically, Coinbase holding onto the Bitcoin Cash (by not supporting it, and hence not letting their users sell it) is probably helping it, since Coinbase users cannot dump their BCC for a quick buck. As you say, it's kind of a giveaway..