Poloniex got itself into trouble by listing unregistered securities and outright scams like jl777hodl, MAID, and Dash.
Their only way out was to make nice with Goldman, so the Goldman-captured courts and regulators would grant them indulgences for previous sins and declare everything kosher.
Going forward, Polo will have the resources to support fulfillment of their fiduciary duties (which includes distributing to users their Calisto airdrops) and will have the deep pockets to sue if they fail in those duties.
Poloniex got itself into trouble by operating unlicensed margin trading and lending services. This is most likely the reason why they are having issues honoring withdrawals because they're an illliquid exchange borrowing coin from Peter to pay Paul. They got in over their heads and the only way out was to pass the buck to Circle.