As long as pro boxers fight without head gear, these things will happen. Even with head gear it would still be dangerous. It's just the nature of the sport.
In the early 1900s college football players were made to wear helmets after five or six were dying every year from violent collisions.
Any sport, like boxing, where violent blows are directed at someone's head will result in the receiver of those blows taking a risk of bad injury or death.