This is my best unbiased summation of the average blue bleeding Kentucky fan.
Its a mixture of several things, but this one really means more than most, as odd as it sounds. UT folks might have to place it in terms of a football rivalry to get the idea. The normal die hard Kentucky fan views Louisville as "little Brother", which they are so affectionately named.
In their mind, (and rightly so, more often than not) Kentucky has always been superior to UL, in every way shape and form. Sure your FROM Louisville, but why like a school like that over your own state school?
When Pitino left for the NBA, I personally was not mad at him, though I was dissapointed. I loved the man through and through, and continued to follow him in the NBA. His draft picks each season, and so forth.
It was when he announced he was going to the "inferior little Brother" that everyone flipped. Lots of people felt betrayed, as though he should never have the audacity to do such a thing. IMO, it was not JUST because it was "louisville", but because everyone knew in their minds that Louisville would no longer be the doormat that they had been for so long. Like it or not, and though they would never admit it, the fear of Louisville rising to the height of UK in the 90's under Rick absolutely scared everyone to death.
Don't get me wrong, UK has always hated Louisville and will continue to do so until the end of time. But when Little Ricky went to UL, the whole world as this state knew it was turned upside down.
So instead of rationalizing anything, instead everyone just hates his guts and Louisville that much more.
This is all just my speculation, of course.