I'm not disagreeing with the principle that you have to eat fewer calories than you burn to lose weight, no.
I'm disagreeing with the statement "To think that people who say diets don’t work aren’t really trying".
In my example, two people are eating the same amount - 1500 kcal daily - theoretically less than the average amount needed to maintain weight (2000 calories a day) but only one is losing weight.
If you can lose weight on 1500 calories a day (without doing insane amounts of exercise) in my opinion you are quite lucky. I mentioned earlier that I could do this in my 20s - ha ha, says menopausal me, bitterly, 30 years later! You have to try, sure, but whatever you might think, you don't have to try as hard as someone who has to go down to 800 calories a day because you can eat almost twice as much.
So someone might go down to 1500 or even 1200 calories a day, be strict on this, weighing and measuring, cutting out favourite foods etc. and not lose any weight. Their diet is not working, yet they are trying. So the OP's premise is incorrect.