i used to work in a fruit and vegie shop when i was younger, and i always wondered that exact same thing.. but when i used to buy bananas.. (since i've had my kids, i'm allergic to them so, i never buy them now) but when i did.. if i wanted a whole bunch, i'd buy them, otherwise just tear a few off an get those.
initially it's a quantity thing..
soem want a few some want a lot, some just want one. :)
when it comes to already having bunches of just 1, 2 or 3.. it comes under the subconcious hygene response.. it represents somebody else already handling them.. therefore, we tend to go for that which appears untouched...
another summary was taken many years ago of the 'single person shopping' as to how many banana's a single person would buy, a large bunch meant they were trying to replace an aspect in their relatiohnships or using them inappropriatly lol a small bunch meant they were desperately looking for soemone to fill their lives and one or two banana's meant they were relatively content and selective in their relationships.