MMA is more ground fighing therefore leaving yourself open to attacks from other people, where as Ninjutsu works standing, on the ground or up above. The most time you want to spend on the ground is 8 seconds. The MMA guys like to stay down there forever, they focus on the one person therefore may get blind sided by that persons friends or with weapons.
Some are like that, there are quiet a few around here also. My Son in Law had a run in like that before he met me. Now he knows that the MMA has nothing on me. :)