Because the weight we have put in is in defense. This is how it is for me, and since we have had similar experiences, this may help:
My weight protects me from men. It protects me like a shield. Scaring off the people who will hurt me, and allowing me to isolate myself from situations in which I feel vounerable.
Our bodies have served us well in that purpose up until now. Now you feel it's time to shed the weight, and with it will come painful memories, you will feel vounerable. So, it's important not to be resentful, and thank your body for protecting you. Everyone dislikes change, but if you can make it through the process of losing the weight and getting to your goal, you can be strong enough to get past your fears.
Remember the poem I wrote about being two people, and being afraid that the intelligent side of me will dissapear when I lose weight? That's another aspect of my fear, and you might have to do some deep reflecting to find what your fears are.
We will be here along the whole way hun!