As others have said, this isn't new. My grandmother was told in the 80s that she needed to lose weight for a hip replacement. She never did it, and died in her 60s from a heart attack.
Right up until she died, she'd been in massive denial about the extent of her weight problem. She said she was "only" a size 16; she could walk for hours so wasn't unfit; she wasn't anywhere near the biggest person she knew; she didn't eat "bad" foods. And she didn't, really. She just ate huge portions and convinced herself they were normal.
But the fact was, she was clinically obese, spent her whole life obese, and died obese, from an obesity-related heart attack. And there are far more people like her now than there were 15 years ago, when she died.
You can see them on this thread, saying their BMI might put them in the obese category but they're not that big, not really.
Which is why it's so hard to do anything from a public health perspective. When you've got 65% of adults in the UK now being overweight or obese, how can you possibly tackle that when a large proportion of those people seem not to think there's a problem?
FWIW, I used to be big. I told myself for years it was just my build, I was naturally that size (big feet etc) and I was fit at the size I was (I was fit - I ran marathons). It took losing the weight and seeing my "new" body to make me realise I wasn't naturally big at all.
What was worrying though, was when I lost weight, getting to an ideal BMI, people were queuing up to tell me I was "gaunt." Being overweight is the norm now. It's positively encouraged, with the whole "treat yourself, here have a cupcake" culture.
Encouraging obese patients to lose weight before operations is a good idea in theory, but in practise is little more than pissing in the wind. The problem is so much greater than this and needs tackling on individual, community and national levels - but nothing can escape the fact that the obesity crisis is primarily down to individuals and what they choose to eat.