"Interactive Brokers noted that, as has been widely reported, the energy markets yesterday exhibited extraordinary price activity in the New York Mercantile Exchange West Texas Intermediate Crude Oil contract. The price of the May 2020 contract dropped to an unprecedented negative price of $37.63. This price was the basis for determining the settlement price for cash-settled contracts traded on the CME Globex and also on a separate, expiring cash-settled futures contract listed on the Intercontinental Exchange Europe. Several Interactive Brokers LLC customers held long positions in these CME and ICE Europe contracts, and as a result they incurred losses in excess of the equity in their accounts. IBLLC has fulfilled the firm's required variation margin settlements with the respective clearinghouses on behalf of its customers. As a result, the Company has recognized an aggregate provisionary loss of approximately $88 million. The Company does not believe that any anticipated losses will have a material effect on its financial condition."
I understand why IB does not want their customers to take physical delivery. Consequently, I also understand why IB customers' positions must be settled at the end price of USD -37.63 if the customers have not liquidated their position before the end of trading at the last day of trading.
What I don't understand is why IB customers allegedly should not be able to trade on the last day of trading. What difference does that make?