At its core, the emotional tension that builds up in the audience (whether it’s others or ourselves) is based on aggression. If you replace the emotional build-up of aggression with sympathy, instead of a release of tension, the audience will feel pity.
As an example, imagine in some context that it is funny for a drunk person to fall on his face. If you replace aggression with sympathy, it will seem more pathetic than funny and evoke pity rather than laughter.
The consistent response to seeing a uni-cyclist is related to sexual development, suggesting that humor develops from aggression in males.