Why on earth would banks need or want Ripple? They can already exchange funds easily using existing centralized networks -- blockchain is useless in that context.
A its a lot faster
B its a lot cheaper
C they can track everything until the money reach the account
The question is more why wouldnt banks want Ripple
Spot on.
"But soon banks will develop their own coin and Ripple will be useless" -- but this argument you can use to anything. Soon Bitcoin is useless because everyone will develop their own coins. Any coin can be replaced at any time with hundreds of new projects. Even if you can do something in theory, it doesn't necessarily make sense financially. Ripple have also tons of banks with them already for a good reason (and probably more coming).