This isnt a career where you put your life on the line only for one fight, you have your whole life to think over. If you have a injury and go into the fight and make it worse, then you might not be the same fighter you were or it will take even longer to heal. and there is a risk of just doing very poorly because of that injury not getting anything out of it, or for the lesser names, getting cut.
if you get injured early in training camp and dont go into the fight fully prepared, your most likely gonna get your ass whooped. and that could possibly even result in more injuries