Coinbase is adding etc. Why etc?

Competition

It’s actually traded on a number of fiat exchanges including circle perhaps Coinbase’s major future threat. Zcash is also traded there.

Previous Fork

They seem partial to previous forks like btc. This makes it easier to add and might allow them to pay off Coinbase holders who were entitled tot he fork.

Publicly traded

Etc is one of two currencies that have a traded trust. Obviously a trust with a large premium might make some people seek out the Coinbase version for arbitrage. Dash has a trust in Canada and a zcash trust would be eligible to list by the digits currency group in sept.

security status

Eth seems like it is too big to be called a security or the sec would have moved by now. Etc is in by association with Eth. Other coins without icos like xmr dash would seem to have a good shot.