One has to have a greater passion for cycling to stay in it, let alone accomplish the necessary to get to Cat-3, Cat-2 and perhaps Cat-1.
It was no different 20 years ago than it is today. Bike racing is not something you can fake. You may be able to delude yourself and others in the 5's but past the 4's, into the 3's and 2's. It's all about recognition and respect thru achievements.
Many are not willing to put in the time, effort and expense that is required. Figuring a training plan that works, then juggling that with the demands of family and career is not for the meek. Nor is it for those who grandstand.
Losing the drive to compete is also a factor, without it it's game over.
What took me out of cycling for the most part 10 years ago was the burn out syndrome. Racing, coaching juniors and promoting a stage race led me to burning the candle at both ends. I returned home after training in France for two months, went to a race, went off the front, turned around stuck the bike on the rack and drove home. Pretty much just played and competed in tennis for the next few years. cycling was only to stay somewhat fit.
At this point we'll see how Sept. rolls around. Full scheduled return to racing is spring 2015. So far I have enjoyed riding and training, which included a few days this past winter riding in the snow. ( probably some of the funniest times I've had looking at drivers looks of disbelief going by me.)
Everyone is different and therefore there are hundreds of reasons as to why some stop.