First, I want to be clear about the word "outsourcing" because many writers today use the word to mean "offshore contracting." In this bank technology context, outsourcing has nothing to do with geography. I'm talking about the banking industry in the U.S. where outsourcing was known, 45 years ago, as "service bureau" or "third party processing" or even "correspondent banking." The outsourcing word was adopted as a modern word in 1989 as a result of the IBM/Kodak deal.
Now, what does Bill Gates have to do with this subject? Simply that Bill stated at a conference, "Technology is still too complicated and we haven't done enough to simplify it for the ordinary citizen." Maybe Steve Jobs has, but that's another blog. In my opinion, Bill's quote applies perfectly as to why banks have been favoring outsource mode in recent years. "Enough already, let the experts deal with it."