blistering machines used in the pharmaceutical industry usually work with some standard sizes, hence the size of the blister. change parts also cost a small fortune, so it makes no sense to have them tailored for just one product if it works well enough with existing equipment. thay being said, a couple of things below in reply to the whole thread, not just yourself.

to add to the list of reasons one would want them individually packaged, it's easier to dispense a set amount of pills in this manner, for medicine that needs to be tailored for each user more often (think if you need 5 capsules, you'd get a blister that is weirdly cut by the pharmacist with a pair of scissors - cutting the blister also removes important information like lot number and expiry date). also, it could have some stability issues outside of the blister, so dispensing them naked in bottles might not be the best thing.

for antibiotics and such, it's also crucial to take each and every dose prescribed so dropping one in the sink accidentally when you're shaking a bottle is something you're trying to prevent. the size of the blister would also make it harder to lose around the house or one's backpack/bag/purse/saddlebags/bag of holding and then not taking your last dose (in addition to the change parts thing mentioned at the start).

individually wrapped bananas are a waste. for critical things like pharmaceuticals, there is more likely than not a good reason for this. look up pharmacovigilance if curious to know more.