I had this too! It's frustrating but at the same time I tried to change the way I thought about it. Lots of people said to me, you're doing so well on the pre-op diet you can definitely just keep going, don't worry about the surgery. I even had that from my husband before the surgery lol I think surgery just seems so extreme to people, and especially if they love you they don't want you to have to go through pain/suffering. Just kindly explain that you're doing great because the surgery is motivating you, but you have tried many things before and it is very difficult to stick to these sorts of diets for the length of time people like us need to, in order to get to a healthy weight. They really think they are helping/showing you they care, they don't realise how frustrating it is lol
Xx good luck with everything, you're doing so great!