Seems to me that the purpose of a martial art and of MMA differ significantly. Most martial arts are about finding a unity and discipline in your life and passing that on to others.
MMA seems to be about finding the movement combinations from various martial arts that combine to cause the most damage to the opponent. I can’t imagine being able to actively practice more than two or three arts at the same time and actually hold to the core principles of all of them.
Takes me back to Karate Kid, really….