Your bank has not done this for your benefit and it hasn't done it in a way that benefits you. They've done it to pass on (to you) the liability for any fraudulent activity.

From http://www.cl.cam.ac.uk/~sjm217/papers/fc09optimised.pdf:

"We reverse engineered the UK variant of card readers and smart cards and here provide the first public description of the protocol. We found numerous weaknesses that are due to design errors such as reusing authentication tokens, overloading data semantics, and failing to ensure freshness of responses. The overall strategic error was excessive optimisation. There are also policy implications."

"The move from signature to PIN for authorising point-of-sale transactions shifted liability from banks to customers; CAP introduces the same problem for online banking. It may also expose customers to physical harm."

Meanwhile, I switched to a bank that uses SMS as a second factor and only where it's necessary: I don't need to use an inconvenient calculator.