No adult should go down to 1200 calories (I wrote about it here: https://medium.com/in-fitness-and-in-health/is-a-1200-calorie-diet-appropriate-for-anyone-e4772ccdb5ac ). And if he/she did it, he/she would lose weight. We simply have people who just aren't good at estimating their food intake.
A team of researchers led by Steven Lichtman looked at people who can't lose weight eating less than 1,200 kcal per day. What they found was that the so-called "diet-resistant" people ate 1,053 calories/day more than they reported.
And if you're all screw you, Egis, I'm good at tracking calories please, know that even registered dietitians have been found to under-report their calories by 223 kcal.
You were not losing weight because you were not in a calorie deficit (even if you think you were). IF helped you to finally achieve calorie deficit. Kaboom — weight loss.
Don't get me wrong — I'm happy you found something that works for you and you can stick to. It's super rare these days. But there's no magic when it comes to IF.