Because the Kentucky Derby is for horses classified as three years old. This means they can only run once, when they are three years old.
A horse named Super Saver won the 2010 Kentucky Derby!
Giacomo won the Kentucky Derby in 2005.
Horse 'Secretariat' won the Derby in 1973.
Orb won the 139th Kentucky Derby.
Kentucky Derby 79 (1953) was won by Dark Star.
A horse named Thunder Gulch won the Kentucky Derby in 1995.
A horse named Foolish Pleasure won the 1975 Kentucky Derby.
A horse named Dust Commander won the 1970 Kentucky Derby.
The horse which won the 1981 Kentucky Derby was Pleasant Colony, ridden by Jorge Velasquez.
Giacomo won the 2005 Kentucky Derby. He won with odds of 50-1.
A horse named Elwood won the thirtieth Kentucky Derby in 1904. Elwood was the first horse bred and owned by a woman to win the Derby.
The 14th Kentucky Derby was run in 1888 and won by MacBeth II.
The Kentucky Derby did not begin until 1875.
Horse 'Chateaugay' won the 1963 derby ridden by Braulio Baeza.
If you are talking about the Kentucky Derby, the horse was Jet Pilot.
The answer is Willie Shoemaker and his horse Ferdinand who won the 1986 Kentucky Derby
Real Quiet won the '98 Derby.
Super Saver won the 2010 derby.
The 1976 Kentucky Derby winner was Bold Forbes
The 2005 Kentucky Derby winner was Giacomo
Aristides won the first Kentucky Derby back in 1875.
Strike the Gold won the 1991 Kentucky Derby, his jockey was Chris Antley
Pleasant Colony won the 1981 Kentucky Derby with Jockey Jose Velasquez.
The horse 'Animal Kingdom' won in 2011.
Horse 'Proud Clarion', with Jockey Bobby Ussery, won the 1967 Derby.