When you (men) spot the object of your desire, the neurotransmitter dopamine lights up areas deep within the brain, triggering feelings of pleasure, motivation, and reward. (Cocaine acts the same way.) You feel a rush, and your heartbeat quickens. Attraction, too, is a powerful drug. The brain stem also gets into the act, releasing phenylethylamine (PEA), which speeds up the flow of information between nerve cells.
Her goals are programmed for the long range; yours are often shockingly short term, right up to and including thoughts of pedestrianophilia. And she knows it, which is why she presses those short-term buttons shotgun-style: She never knows when a suitable mate might be looking.