MMA is not just boxing added in with Kickboxing/Muay THai etc. There's grappling aspects too.

MMA striking in a boxing context is often seen as 'deficient'. But you have to remember that since it includes ALL

 aspects of combat (save for weapons) they have to account for a wider base in stance to defend a potential takedown. MMA striking is a significantly different animal.

Much like MMA Jiu Jitsu is different to traditional BJJ.