While you're right to an extent, the decision of whether or not adding STEEM to Coinbase it's not up to us. I mean, Coinbase is seeking to add a new coin to trade with and if they find numerous people asking for STEEM, they'll look at it and its addition will be taken into account for sure.
RE: Coinbase is looking for the next coin to add to it's exchange, Please Fill this form for Steem