In my personal, anecdotal, episodic, worthless, short sighted, insignificant experience:

In urban areas: - people know few people - most boys are nerds (aka single) - most girls are single - non single girls mate with 5 years older men. - most boys are single - most 20yo men are single

in rural areas: - everyone knows everyone - only 15% men are nerds (aka single) - all girls are paired up - only 10% girls are paired with 5 years (or more) older guys - most boys are paired up - most 20yo men are paired up

Is your experience different? Do you have studies about differences between urban and rural SMP?

But most importantly, what do you think is going on?

my guess is: urban boys leave urban girls free, so girls find men outside their small social circle and in the open sea of the city sexual market place, thereby freeing their hypergamous instincts onto the relatively many wealthy men. So it's both that young boys don't lock them and that girls have better options.

EDIT: By boys and girls I mean teens and by men i mean men between 20 and 30.