It doesn't, the graph is incredibly misleading, instead of dropping off to zero as you would intuitively expect the entire graph is frozen in place making it look like your app is perpetually using the same memory it was using right before it went to sleep. It's an unfortunate display bug and has existed ever since app sleeping was introduced.

As Brody points out here, your app is not consuming memory during App Sleeping. Thank you for the feedback, @brody!

Thank you!