defender putting offense in danger

[jeremy341a]

I was reading an old post about falling before contact on a block/charge Why is it when a defender who is legal begins to fall early many people say "he's putting the offense at risk"? I don't understand this theory. Why is the defender required to stand there and get trucked to absorb the energy so the offensive player doesn't hit the floor as hard. IMO opinion the offensive player is the one putting them both at risk. Now if there is still enough contact or his is being placed at a disadvantage enough for a charge that is another argument.