Boxing is just about the only Olympic competition that uses amateurs in a big money professional sport, largely because it's a highly individual sport controlled by shady promoters and shadier alphabet soup organizations, and even if you could negotiate all that treachery to stage some sort of national championship there's no way pro fighters would do it for anything less than a mega-purse (nor should they given the risk they take every time they step into the ring).
And while the overall Olympics haven't suffered because of amateur boxers, Olympic boxing is terrible. The quality is in the toilet (largely due to a scoring system that rewards you for slapping your opponent) and a slew of controversial decisions forced yet a new set of changes to Olympic boxing. NBC relegated it to CNBC where no one watched it.