From Keith Kizer just now...
As far as MMA contestants going from 3 to 5 round bouts, it is not any different than boxers going from 4 to 6 to 8 to 10 to 12 round bout. We look at skill, experience and match-up.
I am still not really convinced about the reasoning here but there ya go.
His helmet was stifling, it narrowed his vision. And he must see far. His shield was heavy. It threw him off balance. And his target is far away.