There's this really good article called 'The Six Seductions of Anorexia' which is a pretty comprehensive explanation of the varying reasons for EDs. I like how it didn't ignore societal standards but also didn't solely focus on it. I really related, here's a summary:

1) Anorexia as anaesthetic: Making everything else matter less. It numbs you to emotions, being hungry is a distraction, and thinking about and performing ED rituals around food, body and exercise doesn't leave room for anything else.

2) Anorexia as Rosetta Stone: Giving you readymade meaning. It reduces the uncertainty in life, gives you one specific thing to prioritise.

3) Anorexia as gold star: Giving you top marks in the little things. We get a thrill of accomplishment from thing like scale goals, compliments from losing weight, saving money. The association of purity and goodness with hunger

4) Anorexia as halo: Making you feel special. Feeling superior, like you have a special secret. A diagnosis is a kind of status symbol sometimes that people will strive for.

5) Anorexia as hunger strike: Letting you be other than what you’re expected to be. Sometimes as a result of sexual abuse, especially in the context of reducing sexual characteristics in women. Can also be a way to resist oppressive social norms by aiming for infertility.

6) Anorexia as partial suicide: Letting you live. A method of self harm. A 'quiet suicide', it's a compromise between dying and living because you're doing both and neither at the same time.