While the notion of good and bad sweets is largely arbitrary, some things just taste bad. We have Winegums in the UK (the most popular brand is Maynard). These notionally taste of wine (red = Port, yellow = Champagne etc). They don't really of course, but I think they all taste OK.

...there are not as much good tasting ones as there should be, so you'll buy another bag sooner, which means more profit for the manufacturers.
No (rational) company is going to provide a bad product in order to shift more units. A sane consumer will simply stop buying the product. Selling a product, such as sweets, in which some of the contents are 'nice', and some are 'nasty' s equally risky. Unless the nice ones contain some extremely addictive substance, such as nicotine or crack, then the customer will soon give up.

Apply the same logic to floppy disks. If 3Com (or whoever) made 50% of floppy disks physically defective, you'd have to buy more boxes to compensate for the fact that some of your disks don't work. BUT, this only works IF 3Com were the only supplier. As it is, there are other companies making disks (and winegums) which mean you can simply switch your loyalty to a better product.