“Mortdecai” will leave any viewer with a number of pressing questions: who taught Gwyneth Paltrow to affect British? How many jokes about genitalia can be squeezed into a single film? What exactly happens in this mad beehive of plot maneuvers? And most crucially —why would anyone make this movie? But the last one isn’t meant as a broad shot at “Mortdecai,” which is not without charm. The question is not meant to be snide: you really want to know why director David Koepp and screenwriter Eric Aronson decided to make this film in the first place. It’ll practically eat at you.