Probably to do with the fact that there is a perception (rightly or wrongly) that representing his country means more to Rafa than Djokovic.
I am not meaning to attack you or disrespect you as it looks like you quite the tenure and resume here at MTF. But do you really think thats the case?
Nole IS Serbia. Do you realize what winning Olympic gold would do for his popularity? He is probably the most famous Serbian person in the world and definitely in the country. He has his bottled water, his own product, he is Michael Jordan, Barack Obama, Leonardo DiCaprio and Tom Brady all put into one in Serbia. He knows the value of winning this title and theres no way that the odds are what they are because of the perception that he wants to win Olympic gold more than Nadal.
With that being said OP is incorrect. Djokovic is favored to win both Wimbledon and the Olympics.
At Wimbledon, he is 2.48 to win. Nadal is 3.64.
At the Olympics, Djokovic is 2.86 and Nadal is 4.86
I have no logical reasoning for that discrepancy except for the fact that Nadal has not won an ATP 1000 event on hardcourts since 2009. I realize that the Olympics are played on grass, but bookies are saying that Nadal is much, much more dangerous in a best of 5 format as opposed to a best of 3.