There are many reasons these may be pacakaged this way: from lowering the possibility of accidentally taking the wrong pill to anti-theft.
It would be cheaper for the manufacturer to just put them all in a bottle, so rest assured they wouldn't do this if the benefits didn't outweigh the costs.
Adding that certain markets won't accept bottles, you must use a blister.
Why is it one per card, bit of a head scratcher, but given the logistics and distribution costs of shipping this format, agree they wouldn't do this for fun.
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.
Here's the comment I was looking for!
I was going to suggest this might be the issue. (total guess), but it made sense when I saw its the standard size of other blister packs you get.
I also heard that the reason heinz tins dont stack well whilst other brands do is because of how expensive it would be to replace the machines (or parts of the machines) that make the can lids and bases.
So it was a fair assumption that it's basically the same problem here.
Especially when you consider that it's probably very few people that need just 1 of a certain pill.
Thisnis likely a supply issue with this medication in the multi blister packs, so they gave 20 singles.