I didn't realize it but they charge no fees for the first $1,000,000 of Bitcoin payments per customer. That's giving away a lot of profit! Literally the first $10,000 of profit from every customer. They claim to have 36,000 customers that would be $360,000,000 in lost profit. In order for them to start making a profit from every customer they already have their customers need to make $36,000,000,000 first. That's 36 billion dollars in sales before a profit on every current customer. The current Bitcoin market cap is $6,348,864,237. Kinda crazy.
All their customers will not necessarily have a million dollars in sales, IMO many/most will have much less. Also when a merchant accept bitcoin via coinbase on their site they will essentially get free advertising for people to potentially buy bitcoin via coinbase (and have them earn their 1% spread on bitcoin purchases/sales).