The attached research presentation discusses relative conservatism of 2 agencies as well as advantages of simultaneous vs sequential filing: http://www.topra.org/sites/default/files/assets/3-%20Carrol%20Marcus-%20A%20Global%20Perspective%20on%20MAA%20Procedures.pdf

For MNKD, I beleive it is a matter of time, resources, and money. They simply don't have enough infrastucture to manage a sequential filing. The added cost of filing in Europe today would have to be funded by more "minimally dilutive" financing; whereas, if they wait for FDA approval, a partner should be eager to fund and manage the European filing.