> Financial services is particularly interesting as a study case as it is almost 100% information processing, hence fully "disruptable". Why is it not happening?

I'm not sure I agree finance has not been disrupted. I can immediately think a few financial industry disruptions, some even outside incumbents. Fractional reserve banking, credit cards, asset backed securities, online payment providers, regulation, hedge funds are some things that have changed dramatically how financial business (some aspect of it) is done during the last century or two.

One thing that may hide all this is is that the ones currently shouting loudest about disrupting finance seem to have a serious lack of understanding what finance actually is and how it works, and until they do, I don't think they disrupt anything.