When a male climaxes the blood rush he has depletes the muscles of energy that produces glycogen. Since men do have more msucle mass than women they become more tired after sex... plus men are way more relaxed after making love... err boning where most women are not!
cause we don't want to hear you babble on and on afterwards. we only do that in the beginning or make it look like we are listening in order to get some, but once the sex is done, we could care less.