As a banker myself, I take offence to being "broad brushed" like that and being called "identikit".
Lets be honest about this, it's not just the bankers that exhibit this type of herd behaviour, it's the vast majority of the population. Having looked into human decision making processes for a piece of work I have done, it struck me that "herd" behaviour has everything to do with not wanting to be seen to do something controversely to what seems to be the norm. It's not so much about being the only one getting it right, but what if you do something that goes against general belief and you get it wrong. At least when you do something that everyone does and it goes wrong, you were not the only one.
Similar to taking a chance on a new restaurant, or wearing a red jacket to work (Trust me I've done it, the results are quite funny).
To come back to Bankside Mix - I would love to see some more variety, but being as it is, it caters mainly for workers in the surrounding areas. As a result, it's probably a case that the only places that can afford to run on an hour or so a day are the big chains...