Was 2FA enabled? Some people are lazy when it comes to securing their accounts and when funds are stolen, they lay all the blame on exchanges.
How does people gets access to other peoples account in the first place? Isn't it somehow poloniex responsibility to make sure that the account details they hold will not be leak go anyone else but at these days it seem like it did. There are several poloniex reports like this and the accounts owners were not to blame because they didn't do nothing to get their account login detail.
people have a habit of using the same email and passwords over and over and over and there have been many hacks before. so the email and password combinations are already out in the open. YOU are responsible of doing as much as possible to prevent a hack in the first place.... polo should/could also do a lot more by detecting suspicious (like detecting somebody suddenly logs in from the other side of the world) but still.... ENABLE 2FA FOR THE LOVE OF UR CRYPTO'S