Because their dominant culture of 99% defect-free operational excellence squashes any attempts at innovation just like a Sumowrestler sitting on a small gymnast.
He later denied having said anything of the sort wisely perhaps, since the Japan Sumo Association, which can make or break a wrestler's career, does not take kindly to criticism.
The use of physical punishment in the Japanese sporting arena is not new - in 2007 the head of a sumo stable was fired by the sport's national body over the treatment of a 17-year-old wrestler who died after being beaten during practise.