Why do I see cryptocurrencies that aren't supported by Coinbase?

Coinbase provides market information, descriptions, historic trading data, and links to relevant white papers and project websites for cryptocurrencies, determined by current market cap. A subset of those assets can be traded on Coinbase. 

Information for cryptocurrencies not available for trade on Coinbase is provided for educational purposes and doesn't indicate that Coinbase will support any specific cryptocurrency in the future.