Why does my mortgage company want me to set up a separate plan for me to sell one acre of the 2 acres of my residential property?

I only owe 30K more on my home mortgage. If I sell one acre, I can pay off the whole mortgage. Is there a way to avoid having to set up a percentage mortgage payment for selling the one acre, and then turn around and pay off the rest of the mortgage, which I am afraid will increase the amount I need to pay to own my property. I am retired, living on soc sec and a tiny teacher retirement which has me living on 1421 per month and paying 500/month mortgage. I am trying to look at all possible ways to pay the house off to keep from going broke.