Yeah, we can blame the CME.
The CME didn't allow enough time for the internal programmers at FCMs to adapt all of their systems to negative pricing before the skullduggery went on.
It had nothing to do with margins in my view.
IB was fine with handling negative prices the next day.
It seems IB systems could handle negative prices, they just didnt know CL could do it, like someone at IB didnt read the CME memo sent out weeks prior and so no one checked the 'can go negative' check box in the CL backend setup page.
.
Cha-ching!