I am going to say this: if a man goes out with you and then wants to "just be friends" it usually means that he is not physically attracted to you, OR he recognizes that you are on a different page than he is, and out of respect he doesn't want to try to use you or get over on you. Judging by the way you phrased your letter, I see you as a quiet, somewhat shy and unaggressive woman that the guys view as "a nice woman." They know they don't deserve someone of your caliber since they are just looking for a roll in the hay, so they pass you by. Really, though you are wondering what is "wrong" and looking for this situation to be a problem, I see it as fantastic. You are not being mistreated by any of the guys you go out with. They have more respect for you than that, which shows they are gentlemanly fellas. Don't worry about it, just keep trying. And perhaps glam yourself up a bit more. Men don't have much imagination and only see what you present. Perhaps a new hairdo, a sexier outfit will get the one guy you really want to think of you as more than a buddy! :)

Just a curiosity question, but these guys that just become friends...do you really find yourself attracted to them during the course of the date so that you want more dates and maybe even a relationship? Also, do they know they are on a date?

It probably depends on how you're coming off to them. If you're keeping the conversation pretty generic, then they may feel like there's a wall between the two of you. You can make it be known that you would like to see them again, and that you like to see where things could go.