So sad, I remember years ago chatting to one of the top Superbike champs in the pits at Mallory park.
Asked him if he would be doing the Isle Of Mann TT.
He said no it was far too dangerous !!
Seems as he said, driving at fast speed round the tracks with other top class riders you could stay right behind them and know what line etc
they would take, on the Isle of Man at the time there were too many unpredictable amatuers, hence the high casualty rate
Don't know if things have changed these days ?