Why does Cup Series drivers always win in the Busch Race?

last year Cup Series drivers won about 80% of the Busch races. That is my opinion. I want Nascar to limit the number of cup drivers that come to the Busch series to race. What do y'all think. In the Busch races I want to see former winners like: Mark Martin, Jeff Burton, Matt Kenseth, Tony Stewart, Carl Edwards, Greg Biffle, Jamie Mcmurray, Kasey Khane, David Gilliand, and finally Kevin Harvick.