Because the bank expects you to read and understand the loan agreement - in fact, most bank documents state exactly that right before your signature "I have read and understand and agree to the terms and conditions" If you don't take the time to read the loan agreement(or even ask questions) after seeing that statement who is at fault here?

Yes, I think the bank should ethically tell you about possible increases etc. but they are under no legal obligation to do so so far as I am aware so long as they keep to the terms and conditions you signed up for.