I've been thinking about this over the last day. When a trials rider turns 25, he (she) has generally been competing for about 10 years. At that point it's dawned on him or her that they're about as good as they're ever going to get and enduros looks like a bit of fun. They also (if not married) have a bit of spare cash so it's off to the local shop to buy an enduro bike. Lo and behold, trials riders make good enduro riders so they start pulling in some good results. The wheels fall of when the kids come along 'cause enduros is (as mentioned) really expensive. So it's back to trials.
I had an absolute razzle in enduros and, if I could afford it, would do both. But I reached a point in enduros where I was SCARED! And I mean really scared. To get from regular 4th/5th places in fields of up to 200 to 1st you had to leave your brain in the toolbox. This I couldn't do. Believe me, 100km/h 30cm from a barbed wire fence sharpens your mind.