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 they would rather use another exchange like Kraken or poloniex in order to also trade pairs like BTC/XRP or BTC/VTC.
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.