Banks use tools as a store of value by holding some assets in reserves, for various economic benefits. Although, adopting Bitcoin in such capacity, would have it's pros and cons. Obviously like controlling inflationary trends, and even help stabilize the volatility of Bitcoin to its users, and conversely such volatility could also alter the stability of a banks statement of financial position. All these could add up to a more stable global economy. Surely banks have started to think of such prospect
Any Bank that wants to add Bitcoin their asset, shouldn't think of stabilize the market price because they don't have such powers, Banks especially the Central Banks can do well to controlling the activities and inflation of Fiat as that is within their purview, but they cannot extend that to Bitcoin. However, the reason why banks are currently investing and holding Bitcoin is because they've seen how potential Bitcoin can be, initially a lot of them were skeptical in adopting Bitcoin, else Banks would have been the highest adoptors of Bitcoin if they had the foresight.