[C4stor]

But then someone at the bank has to decide between Visa and Mastercard.

And this persons surely thinks "ok, the conditions are roughly the same, what is going to make sure none of my clients even bother to ask why we chose this".

So the bank picks something they know that for sure their clients won't question, and here you are. Even if a newer provider emerged with better conditions, they probably wouldn't pick it because they don't want to deal with the inevitable questions.