May have to do with the fact that he is 38 years old who would move a weight class to go fight a guy hailed as going to be the best ever...who is the biggest LHW and in his prime.
I want to see this fight as a Silva fan. There is no excuse. Anderson stepping in the cage at age 38 or 39 to face the phenom that is Jon Jones at not even a catchweight, would be more legendary than anything GSP has done in his career.
I don't think age is affecting Anderson all that much. I'm certain he's slowed down a tad, but to coin a phrase, the man ages like a fine wine. He's had one lacklustre performance in the past however many years, and he even managed to win that. He's taken so little damage that he's aging far better than most.
As per your cheap GSP jab, at least Georges has never crumbled in the face of injury. Poor Andy hurts his ribs and almost loses a title fight. GSP tears his groin/fights with a flu and injured achilles and still dominates.
I guess we know who the true warrior is