It takes a few hundred ETH to have worthwhile leverage.. so they probably risked losing a substantial amount of trade volume and liquidity with the fiasco aside from loyal customers and early adopters. It wasn't just the natural market forces. They directly manipulated the market by stopping trading, and indirectly during and after the event with a variety of system issues that are not comforting.

IMO this move to replenish traders was a mature business decision that many tech companies would have failed at let alone crypto companies. There is massive money in the long game for Coinbase/GDAX, and providing real and imaginary assurance could cement them to become the Visa of the next decades.