He just hates Fitch, I remember an interview with Ariel Helwani where he called Jon Fitch a baby because he was "crying" for a title shot. I think that was back when Fitch beat Thiago Alves.
Personally I had it like this:
10-9 Fitch (argument that it was a 10-8)
So I convincingly had Fitch winning the fight. Penn also was discouraged and felt that he lost, its a big thing when a fighter doesent try to spin things and admits he should lose.