Luckily I never had any coins in Bitfinex.
Chances are they prioritised convenience over security. There was most likely something in place which just sent a message to BitGo to release the funds, thus being nothing more than a gimmick.
Sadly people will never learn, people will always lose funds to a centralised entity. There are ways to improve on this, like multi-sig that isn't just a gimmick, as well as public audit pages (I run this site and we keep every address we own public).
Honestly, I'm guilty of keeping a ridiculous amount of money in various exchanges, but if an exchange gets hacked and I lose that money, the loss will be a large part my own fault.
If it didn't take so damn long to get money in and out of exchanges, then it wouldn't be so common to leave a stash there for random trading.