I want to see marsupial babies in their mommy's pouch, please!
Seems more efficient. No lugging around growing offspring internally, birth is a breeze, doesn't risk death to the mother during birth and you can just eat or abandon it for any reason. Takes a lot to grow a baby inside of you and marsupials won't get bogged down by them if they are sick, injured, not enough food to healthily supply to the both of them, etc.
I know kangaroos do it and not sure how many more if not all marsupials can but after giving birth to one joey, they can pregnant again shortly after. They keep the embryo on standby in case something happens to the first one. Marsupials have their own backup hard drives.