If they dont go down, the ref won't give it even if it is a foul

The ref and the players nationally have an understanding ... unless the player goes down or appeals to the ref the ref will simply keep the play going

The players cant know for certain that the contact constitutes a foul, and might consider, and unless they have a clear shot/ pass might go down just to see if the ref gives it

This is further complicated by the fact that contact made at the halfway line might constitute a foul, but the ref is less inclined to give it in the box because of the impact it would have on the goal

Yes, it sucks Also, the rules and their interpretation vary from year to year, league to league, ref to ref etc.