It's easy to see why this is the case: it's another, unexpected, result of ever-increasing regulation in financial markets. The best and the brightest are often driven to innovate, but if regulation becomes so stifling as to reduce the opportunities (or perceive opportunities) to innovate then those with the drive will go elsewhere. Having worked in banking, I can assure you that the environment is often (though not always) very stifling. There is often a constant pall over the entire organization...stemming from the constant sense that you're owned (in every way that matters) by the regulator, and that the "free market" as it pertains to the financial world is, in fact, largely an illusion. In fact, in one position I worked in, most of our efforts where directed at satisfying the regulators NOT producing any analytics of value to the business.

Now I recognize this isn't true of all financial institutions, and I suspect those that survive and thrive will be those who innovate effectively even within the stifling constraints of recent regulation. That said, it's just become a very difficult space to work in, especially in comparison to the freedom offered by the tech space.

Please note too, that I'm not arguing whether or not the additional regulations were necessary and effective; I'm simply stating that they are having the effect of raising the cost of doing business for financial institutions, and also tightening the constraints they operate under which has the indirect result of making it difficult to innovate, reducing the desire among the best and the brightest (i.e., those who I suppose might be the most driven to innovate and harvest the appropriate rewards for their efforts) to work in those institutions.