Why developer remove their App from App store?

Please correct me if I was wrong, I think, keep an app stay active will not cost too much from developers' time and effort (also the money).

So, I am just wondering that why do developers remove their apps from App store (rather than just keep them alive since it will not cost too much)?

So they don't have to maintain them (e.g. New iOS version compatibility etc.)
Why developer remove their App from App store?
 
 
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