There isn't a point of eating 200 calories to lose weight, most of the people who do it have reactive binges and don't admit it and will get mad that I said this. With rare exceptions even very thin people can continue losing weight at 1000-1200 calories. The people on here who brag about eating under 500 always and never going over it to make everyone else feel bad are a minority; having an ED/anorexia has never been about your daily intake, but about losing weight long term and staying at a lower weight.
As to why you dont lose faster at an intake lower than 500, it's because of the law of diminishing returns/starvation mode. It takes calories to digest food. If you aren't digesting any food, your digestive system shuts down and your TDEE drops accordingly. There is no point to eating so little, at all. You may as well eat at least a little.
I agree with a lot of this, I eat 300-600 cals per day, with one high cal day per week (900-1000), & the only reason I eat closer to 300 on some days is because of severe anxiety & a need for control brought on by dealing with PTSD,& digestive issues from celiac disease (since I was nine the drs kept misdiagnosing me, at 29 I got the final diagnosis of Celiac disease. I am now 30.)
I am a dancer,& I feel so much better when I eat closer to 600.
I am gradually trying to up my cals to 400-700 per day.
I weigh 81.6 now.