The main reason (why banks don't like btc and other cryptos) is the loss of profits. Transactions made via blockchain kills transactions made via banks. But the topic is essential! It should be upped!
It all boils down to business. Banks are afraid that soon a big chunk of their business volume can be affected because a good number of people are shifting to cryptocurrency or to those companies that are involved with cryptocurrency. It is all about fighting for your own kingdom or captured market. Consequently, many leaders of the banking sectors are painting some negative spins about Bitcoin and cryptocurrency in general. What these people forgot is that they are actually the very reason why Bitcoin came into being...on their failure to stop the many financial crisis the country experienced in the past.