Most people consider their bodies a container that they inhabit. Even if you don't believe in souls or have a spiritual concept that you hold to be true, many people believe that personality defines them, not their physicality. Our parents reinforce this idea by telling you that people should love you for who you are, not what you look like. In fact, many of us are insulted or feel that others are shallow if they form judgments or consider us desirable only based on our bodies.
There are good reasons for these feelings, and many of them are based on the inevitability of bodily change. If someone loves you for your beauty, it will inevitably fade. Also, humans experience fatigue in regards to the appearance of everything in their lives. The thing which was so incredibly beautiful or attractive the first 100 times you looked at it soon becomes mundane. We cannot continuously maintain the same level of appreciation for something which we found physically appealing. Eventually, the value of something based on appearance alone diminishes to zero. Even objects which we loved the look of, like a favorite stuffed toy that we find cute, tend to be infused with value based on the emotional attachment we feel rather than maintain their initial appeal based on appearance alone.
Because of this natural tendency, we value people based on character because such attributes are more complex and we are less likely to find that they lose value through time. That being said, even positive personality traits tend to be taken for granted through time, and we have to work a bit to keep their value in mind. Fortunately, absence and contrast (comparing one person's character to another) tend to help continually reinforce the value of things like a person's patience, kindness, and intelligence.
It's natural that we see ourselves as being represented mainly by who we are, and not by the container that we present ourselves in. Certainly, we all realize that society and strangers are going to reach conclusions about our general appearance, but we tend to believe that the factors which represent our character and habits such as professionalism in dress choice, cleanliness, grooming, etc. are what "should" be valued rather than our inherent beauty or lack thereof.
It would take a conscious act on the part of most mature (or overweight) people to change their values in order to place appearance above character, particularly if you are older since younger people tend to be more appearance focused. For those of us who have deeply embraced the notion that character is far more valuable and worth developing than the body, there may be an inherent sense that one is being hypocritical in expending so much energy on weight loss. If beauty is only skin deep and character is what we should be valued for, aren't we acting against our values if we place so much emphasis on our bodies?
This is something that I have not wrestled with much because my motivation so far has been the reduction of my physical pain and to achieve mobility such that I can live a relatively "normal" life. At around 260 lbs. at present, I am likely within 3-6 months of reaching a state whereby pain and mobility will no longer be as strong a goal for weight loss. After I reach the general range of 200 lbs. and lower, it's almost certain that appearance will be a bigger factor, though there may also be health issues as well. Of course, improved appearance addresses my third motivation, avoiding weight-based discrimination.
At any rate, I can't help but at least acknowledge that as someone who values character and is quite indifferent to the outer shell of a person, my focus on my body is perhaps hypocritical, though frankly, it is also understandable. I have to live in this world with all of the disadvantages that are applied to me for being fat. I may not care about the look of bodies, but as long as nearly everyone else around me concerns themselves with mine, I really have little choice but to concern myself with appearance.