In the 1970's there was a slew of Triple Crown winners after years of no horse winning, followed by a lack of winners that continues to this day. Is there any reason for the large number of winners in the 1970's other than pure coincidence?
I just read this article about it.
Seems to be several factors, the biggest of which are todays horses simply don't run 1.5 mile races with the exception of the Belmont, so that final race is a complete crapshoot. Also, despite the criticism Cal. Chromes owners got for "whining" about the Belmont winners skipping the Preakness, he kind of has a point. In the 70's all three races basically had the same field so no horse had the advantage of being less tired.
And just speculation on my part here, but I am sure modern drug testing has had some affect as well.