Commercial banks hate Bitcoin because this will replace current financial system and offer more efficient and cost effective and faster transaction with more freedom.Banks use people's money from deposits to invest in other schemes to earn much more once Bitcoin goes mainstream there will not be only Bitcoin but also many digital currencies will put banking system in danger.
I think this might be one reason , banks use the deposits to invest it and make profit, but they use only fiat currencies till now, they have doubts about bitcoin transactions and thought it's "virtual" enough to be risky