I Think alot of it is due to the huge amount of money paid out in the Futurities its into the millions of dollars now. People just don't want to take the time to train colts for more all around type horses because they want to work 8 or so colts at a time to get two that they can ride for the big money. I'd really like to see the Futurities be changed to 4 and 5 year old horses rather then 3 year olds. But that's a whole nother subject and thread maybe.
I get a kick out of the "aged" events being for such relatively young horses but considering that they are started in their 2's, so many are washed up by 6.