Maybe the Iranians wanted some proof that their money was being well spent. I can't imagine that their observers in NK were too impressed with the launch. I'd hate to be the NK engineer in charge of the project right now (if he's still among the living).
When Iranians are involved, the fear is the failures were intentional - Iranians looking for our interference and/or response or some such. Iranians love strategy for it's own sake - when they're involved, nothing is as it seems. That said, the N.Korean failures were most likely incompetence...