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
Let me tell you things that banking systems do behind us, some of the Banks is trading with Bitcoin without the concept of their customers so for them to do that it is obvious that many of them is serving bitcoin or holding Bitcoin as investment plan in order to make a profit, but they will not make it open to the awareness of government so that they will not be sanctioned because someone of the countries government is not adopting Bitcoin in their country so that is why so many banks do not make it to open when they are holding Bitcoin as a store value to enlarge their banks
It should be noted that investing in bitcoin by institutions and companies is inherently complex and not as easy as it is for individuals, let alone banks and government agencies. Entities are subject to strict regulation and compliance by central banks and governments.
Not to mention, they have boards of directors, shareholders and all decisions must be based on consensus. No one has the authority and right to make unilateral decisions without consulting the shareholders. Therefore, there’s no such thing as banks quietly investing in bitcoin and ignoring central bank regulations.
Organizations and banks have hundreds of ways to generate huge profits from their business operations. They would not be foolish enough to risk their future by ignoring government and central bank regulations just to invest in bitcoin. Bitcoin really doesn't matter to them that much.