Sometimes it seems like your supervisor wants endless changes. You fix the things they said to fix, and then they tell you about more things to fix. Why didn’t they just tell you about all the problems in the first place?
Well one reason is that they know that there are big picture things that need to be dealt with before the small picture things can be addressed. Some problems might not become apparent until the biggest picture things have been dealt with. And they also know that all writing, needs multiple revisions.
Learning to look out for big picture and small picture stuff yourself will help you improve the drafts you send to supervisors. This webpage at the Purdue University OWL website gives a good explanation.
Higher Order Concerns (HOCs) and Lower Order Concerns (LOCs) in writing
Purdue Online Writing Lab