Nothing really.
I also wouldn't call it robbing -- they simply had to adapt to new KYC laws ( Know-Your-Customer), which means that every customer/user on their site need to have a passport/ID added to their account, if you don't have it, your funds (like mine) are stuck, and only become accessibly after adding said ID.. There's been some outrage but there's still tons of people using them.
I don't think they have added claims that the funds are no longer yours after X days, -- right?
Well yeah, that's the point, it was rather unexpected. I believe they simply on one day froze all the unverified accounts, without any prior notice, see https://steemit.com/bittrex/@penguinpablo/warning-it-seems-bittrex-is-disabling-accounts-for-no-apparent-reason
If you're looking at competing USA exchanges, like poloniex, you can argue that they are indeed handling the same situation wayy better, giving users a lot of time to withdraw funds / upgrade their accounts..
https://poloniex.com/press-releases/2017.12.27-Notice-to-legacy-account-holders/