I haven't read all the comments, but I'm going to answer.
For me, I think you get to a certain level and your body gets comfortable at the amount of training and it takes SO much more to drop any pounds.
I'm 5'3", 157 lbs (overweight by 10 lbs for a healthy me- my doc will wrongly say I need to lose 25- which I cannot maintain without starving myself).
Anyway- I've done 2 Ironman triathlons. I am currently training for a 3rd. I can't possibly train any more than I do. I eat a plant-based diet, so I don't eat junk. I have to eat to fuel. It's hard to over-eat on plants.
I can't lose this 10 lbs to save my life. I need to. I'm still chubby in my thighs and my middle. I do strength training, cardio, yoga, and yet the pounds just don't fall away. I think that when you get to a certain level, it's really hard to do more to challenge your body.
When I first started working out and doing Weight Watchers, I dropped 30 lbs in 3 months. I was running for the first time and it just melted away. It's just not as easy now. I'm also 40, so age probably has something to do with it, too. It was much easier losing weight at 30 (and I know it only gets more difficult with age).
Just my thoughts on what I observe from me.