There’s two things which occur to me about your story - and well done, by the way, for taking control, losing the weight and keeping it off.
The first thing is that you responded to direct, clear communication. The fact it came from your doctor may be a factor, or maybe not. But just be aware that not everyone responds in the same way as you did. Your wife may not. Or she may.
The other thing - and IMO, the more important thing - is that once you got the wake-up call, you made a plan, followed the plan, job done. You are, by your own admission, still fat, but sufficiently less so to make a massive difference to your health and quality of life. Fantastic….. BUT…… you had (unless I’ve got this wrong) never tried to control your weight before, and the very first time you tried, you achieved a substantial weight loss and have kept it off.
That is a very, very different scenario from your wife’s - and from most women, to be fair. Your wife has been going to weight watchers for decades and not losing weight. Why do you think that is? Do you think she doesn’t want to, or hasn’t really tried? That’s possible, of course - but personally I think it unlikely.
The reasons are complex. People have suggested hormonal issues, perhaps menopause. At her age that will be a factor, but the fact she has been going for decades suggests to me there is more at play. A good chance that she is using food as an emotional coping mechanism, or is addicted to certain foods, or both. The result is - it will be far, far harder for your wife to lose weight and keep it off than it was for you, and she is probably utterly demoralised by decades of failure. And she may not be aware of all the forces arrayed against her, she will be buying into the corrosive fiction that if she only tried harder she ought to be able to do it.
It IS possible. Some people do it , although the odds are very, very low, hence the phenomenal popularity of WLI, which are giving hope to people who have tried so hard for so long and failed.
I have done it, without WLI, after 5 decades of not doing it. Like you, I’m still fat, but the over 8 stone I have lost has made my life completely different. However, it took a LOT of self compassion, support and damned hard work to get me here, and (so far) keep me here. Oh - and a fair amount of knowledge as well. And I don’t mean knowledge about calories, TDEE and all that stuff.