Retail banking locations are a market-share grab. They want to make it as convenient as possible to put your savings in a bank, because then they have access to your deposits, which can be loaned out as a lucrative product.
It's much like the Chrome Omnibox or Google Toolbar for Google, or the Facebook mobile app. These derive no revenue, but they make it as convenient as possible to use the company's products. That user attention can then be sold to advertisers for a nice profit.
Ditto Hacker News as well - your comments here don't benefit YCombinator at all, and they have to spend money maintaining & moderating it. However, insightful comments on HN attract intellectual people interested in startups, which are YCombinator's prime customer demographic, and so your contributions here are effectively very cheap advertising for YCombinator.