Disney+ buying from or selling to Marvel would not show up as profit or loss for Disney.
Making up numbers:
It costs Apple $800 to make a MacBook. It "sells" the MacBook to Apple Retail for $900 wholesale. Apple corporate now has revenue of $900 from the Mac it sold.
Apple Retail sells the same Mac to the end user for $1000. Apple Retail now has revenue of $1000.
Apple Corporate claims revenue of $900
Apple Retail claims revenue of $1000.
Apple claims a revenue of $1900. But it has to back out $900 of revenue so it doesn't double count it.
Apple wants to show that Apple Retail is profitable.
I used Apple instead of Disney in the example because it is much simpler to show one item being transferred from Apple to Apple retail than it is to show a group of movies being transferred to Disney and Disney selling a subscription.