Lots of reasons: Health - Raised awareness as to the effects of cumulative damage Better money - they don't need to fight anywhere near as much, many oldtimers had other jobs on the side. Big names in boxing make more in one fight than many did in a career back then. Promoters not working together - Golden Boy and Top Rank being good examples. Too many belts - Makes it easy to duck opponents when organizations unfairly rank fighters for financial gain and such. It's easy to not take on all real challenges, and thus fight with much less frequency.
yea id agree with the money most of all. which is why i dont understand why sometimes people get mad when some say that old timers could whoop some of the top fighters today. i think its true. hungrier, fight harder, fight without regard for health or looking pretty makes a fighter a helluva lot more dangerous than an adrien broner. the more you fight, the sharper you stay the better you are. Sugar Ray Robinson would friggin fight every 10 days sometimes!