Most people don't know that today, because most people don't ride bumpy animals, they drive smooth travelling cars. They also don't have to work half as hard as people did back then. I am sure breaking hymens was much more common then than it is today. And if it was more common, more people were probably aware of it. And if people were aware of it, then we may be able to come up with a reason why the verse requires that the father go to the elders of the city first, rather than just gathering up the gaggle of guys to stone her.