Human beings are mammals. Mammals (and all other animals) have instincts. One of the strongest insticts is procreation. Nature favors animals with the traits most likely to perpetuate the species. In humans, these traits include, among other things, physical strength and resistance to disease (leading to longer lifespans). Absent modern sociological influences, the most important attractor of men to women is physical appearance, i.e., a natural tendency to select a mate who has desireable traits for improving the species' longevity. Obesity is not attractive from this standpoint. When we were primitive, the positive traits of caring, sharing and intellect were less important than they are now.
What this means is that, if I, as a male, am in the market for a mate, the first thing that will attract me to a female is appearance. Not just facial beauty, but the overall fitness of the female. That's what initiates the relationship. It's a bonus if the female is intelligent, witty, caring, and not psycho.
Bottom line, it is indeed a cultural prejudice, but I, for one, am not going to apologize for it. The preference for one who is physically attractive (for either sex) is completely natural. The social pressure to suppress these instinctive feelings is no more valid than the tendency for society to treat attractive people better, which it clearly does.
You say you are beautiful. Great! It reminds me of a hat I saw a guy wearing one time. It said, "I may be fat, but you're ugly, and I can diet." You are on the fortunate side of that equation (however politically incorrect it may be).