An average man who sends 18 messages to women his own age can be 50% certain he'll receive at least one response.
For women, they need to send only 5 messages to be 50% certain they'll get a response.
Looking at higher confidence levels, if a woman wants to be 90% certain she'll receive a response from a man her own age, she'll have to send 13 messages. Finally, to be 99% certain she'll receive a response, a woman must send 25 messages to men her own age. This leads us to believe that one potential cause of the disparity between the male response rate and female response rate is the system itself.
If men must spam women with messages in order to elicit a response, then women will be more selective when responding to the surplus in general.
Since women are understandably disinclined to respond to all the messages, men must send out more in order to guarantee any response. Everyone is acting in their own self interest, inadvertently leading to further imbalances in the system.