Kentucky is the bluest of bluebloods.
They had two Final Four appearances in 2011 and 2012. Nothing until now. Before that it had been 13 years and during that time period they made 3 in a row. Then before that they had one 3 years earlier and then before that 10 years when they made 4 in 6 years. Then another gap...and so forth.
Houston had a much bigger gap than most, but again I think conference affiliation is the #1 reason why.