Why did they suddenly change their stance?
Not at all. Just they don't want to look different from their competitors and probably eyeing the fees they can charge from other investors (and futures' gamblers) and, why not? maybe also eyeing a little towards investing themselves...
They most probably have a big board that takes the decisions and probably a few voters have indeed change their mind. But overall I don't think that anything special has change. Keep in mind that they're still part of the traditional banking system.