They sold 15 million copies, 15 million, can you imagine how many people that is, It would take half a year just for you to count to that figure, it's a lot of people, and when a beta platform as secretive as this game was probably tested on hundreds, maybe a few thousand at most, with hundreds of concurrent connections, there just isn't any way to properly predict what a figure like 15 million people would do to the system, it's not just the servers, it's the database behind that running the show, the internet connection having to handle it all, there are so many factors, and you could bring up the fact they made all that money in the first few days, but they couldn't provision the hardware up front to handle that not knowing for sure it would be that successful, and even if you could, it's still a mental amount of resources, especially when you only get 16 people per 'server'.
Its a mind boggling problem to solve as an it project, and don't someone mention can't the cloud provide the resources, we are talking about more than a quick order to amazon to spin up some vms.
i guess if you can't understand why it can't be easy now, you never will, just like I could never understand how you can't get the trains fixed before they've even gone wrong
just take it from me, it's a nearly impossible thing to get right and predict.
It'll get better, they'll work out how to fix the issues they're now seeing with real people hammering it, and as time goes on, less and less people will be on it anyway, easing up the systems too.