Weird. Coinbase allows you to use your debit card, credit card, direct wire of USD from your account (at least in USA). No idea why would they do that -- am I missing something?
Maybe it's because we're outside the USA, but it's much easier to buy bitcoin directly using other services than Coinbase, and we haven't found one yet that does ethereum.
Maybe they would rather use another exchange like Kraken or poloniex in order to also trade pairs like BTC/XRP or BTC/VTC.