A proper corporate database with the security it needs and the amount of people accessing it (remember how many people bought Minecraft) yes it would be expensive to have multiple databases doing the same thing.
If people haven’t transferred would they be accessing it? Not much incentive for people who already transfered to go back to just claim a code, and people who haven’t yet probably aren’t going to be logging in all the time.
No it wouldn’t, millions of people bought it but the vast majority migrated, even if there were still millions of people to migrate this wouldn’t get hit very hard because people would not migrate all in one go, so any simple master+slave database system would work, even an SQLite is capable of handling this volume. The total cost of this would be less than $100 per year if they wanted to outsource everything (which is essentially nothing for Microsoft), if they used any of their existing servers for it the coat would be a lot less possibly very close to 0.
Its Microsoft - they offer multiple DBaaS themselves.
But it costs a lot more than $100 in man hours to properly propose, approve, and implement any production system.
Yes, but it also costs as much to sunset a system, so they spend that money regardless.
