There are few reason why:
1. Bitcoin can compete with fiat, especially for online payment solution. With bitcoin, you can be anonymous & avoid big fees from bank, also bitcoin transaction is usually faster. People won't use fiat if they see advantage of using bitcoin.
2. Government don't like seeing their people using bitcoin, because they can avoid tax, fees & couldn't be tracked easily. So, they won't let bank or anyone to use or accept bitcoin. That's why most bank don't accept bitcoin.
3. Most bitcoiner won't use their through bank for various reason, such as you can't control your bitcoin or you're being watched by bank. Most Bitcoiner will use bank if they want to buy/sell bitcoin only. Bank can't get profit too much from it.
4. Banks are greedy & bitcoin is open source, so they make their own cryptocurrency & control it to get even more profit. Few banks already made their own cryptocurrency, but i think it's just like scam altcoin
Please correct me if i'm wrong
Thanks for the comment. Then no one correct no one here. Everyone has its ideas and is free to express those. Very shortly:
1. If bitcoin compete with fiat the customer will remain the same with the bank. Explanation of this is in my main post. Then no loss if customer stay. You cannot be anonymous if you will use the bank so your second sentence have no sense. Third sentense same explanation with the first.
2. If bitcoin will be regulated it will be not more possibility to avoid nothing legit. Or better it will the same possibility which the people have with fiat money. Exactly the same. If bitcoin will be regulated the banks have no sense to not use it (I think) because of the reasons given in the main post.
3. If the bitcoiner will not use the banks it is another thing that have nothing to do with the aim of this thread. Here are discussed why the banks (must, can) hate bitcoin. If the bitcoiner use itself its bitcoins where is the bank here?
4. It is not possible that every bank make its crypto. Have no sense. How it will be the change of money between banks if this become true?. Maybe are 100 000 000 banks in all the world. Have sense that each of those have its crypto? To not tell that this activity can be hard to manage and totally out of the work made normally from a commercial bank.
These are my thoughts about your post.