It doesn't charge a flat fee for buy/sell crypto currency, but a 2-3% fee based on the transaction value.
So even though I'm sure they've been making cash hand over fist this past 12 months, it makes any sort of future prediction extremely difficult. They not only have to predict customer growth (which leads to transaction volume), but also the price of those cryptocurrencies. It's akin to calculate position from nothing but a accelerometer, and that double integral would be quite a bit of margin of error.
But in the end it may not even matter, as far as revenue growth and even profit wise I'm sure they are doing absolutely amazingly.
Hell, I wouldn't even be surprised if Coinbase has higher daily revenue (definitely more profitable) than Uber at this point.