why does this make me feel better?

Someone close to me has an eating disorder and her comments about it are pretty similar to yours: it’s about control. She used to feel like she had no control in every aspect of her life, so she started controlling the only thing she could, eating (or actually, not eating). The thing about it tho, is that you’re actually losing control of a whole bunch of things by doing that: your health takes a hit and you have to deal with the repercusions of not eating (in your case your parents sending you to rehab).

It’s really hard to overcome an eating disorder (seen it, suffered it myself), but you could try to ease up on it a bit for your own sake, as in, yeah, if you don’t want to eat just eat less than normal, that way you save yourself the travel to rehab. In the end tho, looking for help would be the best choice, but it has to be your choice for it to count.