the reason will be simple the banks are not supported for cryptocurrencies that's why they don't accept cryptocurrency users to be a part of their development otherwise there is nothing in this because we don't need banks are to be part of this field.
If you are new to the market and if someone is planning to invest in bitcoin, the common thing anyone would do is to use his bank account to transfer money to any exchanges where he can purchase crypto currency, other than that what option does he have, you can get bitcoin or any coin in the market through two ways, either mine the coin or you purchase the coin and i am not considering any other option simply because working for bitcoin is not an viable option for a causal user who wants to invest in it, so banking relations are important for a sustainable market situation.