So the money came from other divisions, not gaming alone. So MS didn't make the money back, that's not how it works.
Yes, companies reinvest the money they earn in other areas. But for an investment to make sense, to be successful, the investment itself needs to cover its own costs in order to be sustainable, and to justify the purchase/investment to your investors. You can't just say "Ah, we both this expensive thing that we though would pay itself in 5 years but didn't. But hey, don't worry, we are making money elsewhere".
70 billion is an insane ammount of money even for MS. It will take more than a decade to make up for that. You guys take these things too lightly.