Or because the other Uchihas prefered to stay in it to protect against attacks from behind. He was an edo and it was a 3v1 so the predicament presented no real threat. Madara prefered to be inside his Susano because there was a small chance the 5 kages could pull a cheap trick and seal him. Sasuke unlike the other two isn't an edo and so obviously wasn't going risk being injured because out of arrogance he decided to summon the Susano behind him and not around him.
He can't use perfect susanoo how is this even an argument, yeah 3t he was a master and MS master but there are higher levels with more power he still solos tho