mrbb, yes, but those sharpened rocks were the sharpest edge known to man. If technology has moved on, it took a LOOOOONG time for it to do it!
I cut myself on flint once, only a small thing, but I just turned to a friend and said, wooah, look at that, can you imagine something like that being wielded by a caveman! Now I knew flint was sharp, I learnt that at school, but it just made it instantly clear to me at that point. I popped on here to get a better understanding and it is good of you both to take the time to do so. I looked about a fair bit, but it is not always easy to find what you need. Moving around the internet adverts, and many articles are just that, the latest sales spiel tells all, but often not what you want to hear. I was aware that arrows could be deflected, as with rifle rounds, but assumed due to the bolt length that it would remain-ish on course, but yes, movement of the animal and all sorts will play their part, even prior to strike.
The fact that mrbb sees them as disposable is of note to me, as that is something that I did not see elsewhere. Perhaps that information is out there, or the majority do not look that way, but it is good to know. I'm sure more than a few sellers of broadheads and other equipment show the thumbs up to that one! I do understand the perspective from that outlook though, as stresses will be there. Many shooters will change their barrels after a certain amount of shots for the same reason. I had heard of people weighing, balancing and checking, as even slight differences have a ballistic emphasis over time and distance, so see the sense. I would guess more that the re-using factor comes down to a value for money outlook by the majority. Perhaps partly a "well it worked alright last time" attitude. I don't know if there are a LOT of crossbow bolts and arrows out there, that have been lost like golf balls in the brush.