Well, if they're market players, they'll only put in a BTC buy order when the BTC price is dropping. If BTC value is rising, they can pocket the BTC, and happily pay less cash than the coins will be worth in the future... As long as they have some bankroll (which they appear to), they should be fine.
This is just another business model and they really don't need to be a payment processor to play with that, they just need to have some bankroll to trade/speculate. And what if the price won't go up? What if the price plummets and will stay down for days or weeks or forever? I'm not sure if they want to add trading speculation complexity to everything they need to deal with. These are entirely different business models and I'm not sure if they're even compatible - trading speculation risks/mistakes could easily kill the entire business. My understanding is that their best bet is to try to make exchanging BTC to fiat as secure for them as possible, i.e. to try to exchange always at the price they locked for the customer - do this job well and the volume will take care of their earnings.