How come my husband wont let me have elective surgery?

I just don't understand. Other people's partners are so supportive. Since getting pregnant and having post natal depression I am 40 kilos overweight and have been for 2 years. I have tried to get motivation to lose weight but I just don't have it. I ask him about gastric banding and similar procedures and he just says no straight away, he wont even consider it. I hear of other people's partners being so supportive and I just dont understand why he is being this way. I'm not even saying I definately would want it but it would be nice to have the option! Any idea why he is being like this?