Well women generally have to worry about their personal safety in ways that men do not, so I suspect that is part of the reason why they lean towards package tours. There are places I would not necessarily be comfortable visiting solo that men might be more confident about.

Saying men are more into exploration and adventure is a baseless stereotype however, Sprint. And while your anecdotal evidence may be different then mine, as a woman traveler I have run into many, many women travelers both solo and in groups. I don't think you can really make a wide assessment just based on what you personally have seen in your own little sphere.