Small kids are not as good as verbalizing what happens. Meaning, at the age when this all starts, they will not put it into words like this.
There is also strong cultural assumption that if coach is tough it is good. When kids are complaining, typically unable to explain exactly what the issue is, they are talked about as spoiled by helicopter parents or oversensitive moms.
So, even parents who eventually take their own kids away dont treat the whole thing as systematic abuse issue - they talked about it as personal preference of the kid.