You must have never had a deep bone bruise. They can be considerably painful.
I've had kidney stones, ruptured disk in my neck, torn ligaments and several broken bones but the only time I ever collapsed from pain was from a hip pointer (basically a severe bone bruise). I got speared from behind on a punt return. Dude put his face mask into the backside of my hip bone. I ran about 2 or 3 more steps, the pain hit and I just dropped. I couldn't stand up straight for about 45 minutes. I played the next week... a little.
In other words,bone bruises HURT LIKE HELL...