Correlation is not causation. It had nothing to do with the place. He simply couldn't adapt to the octagon, he fought in K-1 in 1996, then he was an amateur boxer from 1996-1999, K-1 from 1999-2003 and Pride until 2007. His entire arsenal was adapted to the ring.
His footwork didn't work in the octagon because he couldn't trap people in the corners and set them up for kicks. His offensive footwork was always plodding forward and in the UFC people would just circle away from his left. Just watch the Sanchez fight, Sanchez circles to his right, Mirko follows the exact same arc instead of cutting the space. If Sanchez wasn't so terrified, he could have circled away easily for 15 minutes. Kongo did the same thing, JDS, Shaub, etc...
He was always arrogant, and he went to the UFC at his peak of popularity and feared reputation. He didn't train for elbows, didn't train in an octagon, he thought he could waltz in and KO everyone. Gonzaga's KO destroyed his leg, his confidence and ruined his aura so even though he tried to fix those things later on (brought an octagon in his gym, etc), it was too late, the damage was done.