There's usually plenty of profit to be made when you can manipulate the network's hashrate. I don't think anyone runs DDoS attacks just for fun, they're expensive (and illegal, I suppose). If you can bring down a few pools fast then the total network hashrate goes down, and as soon as the difficulty adjusts you can quickly point loads of your hashrate (both from your farms, and the rented miners' from nicehash/etc which still sells for the ~ same price it used to before the diff drop) to your private pool (or someone else's, the one you didn't DDoS'ed) and make lots of coins fast.