Responsive desire is basically the thought that desire is a response to some stimuli, and many females take a lot of work to desire you, because their base level of desire is so low, that they need a massive amount of external stimulus — you — to have sex. Testosterone is key here.
Responsive desire is basically the same process in both men and women, it’s just that men have a much higher level of response built in. Think of desire as a wave, and it has to crest a certain peak for that person to have sex. Men have a much lower shoreline, and for some men it’s always under water. Except during the refractory period.
Now, there is the natural rise and fall of the waves, but there are also external factors that can cause waves, like boats and earthquakes, or charm and physical stimulation from the opposite sex. It generally takes more of these external factors to get the waves over land for women.
But, the longer a person refrains from having sex, the more water gets under the wave. Some people will build up enough water all on their own to have sex, while others never will. Basically, think how long it takes you to start masturbating with no external stimulus. That’s your natural wave cycle, which is then acted upon by others.
And even though a person’s desire can be triggered by an external source, it still needs an outlet. If you only have one outlet, your partner, then that’s where your desire will be unleashed on, and your threshold will stay lower. However, if you have multiple outlets, via porn, a harem, just knowing you can get laid anywhere — most women, some men — then that threshold gets even higher.