Shower Curtains and their rings

Okay, so you know how when you buy hot dogs, and there are like 10 hot dogs in a pack, but then when you get buns, there are only eight buns? Why do you think they can't work things out like the shower curtain makers and shower-curtain ring makers have been able to do? I mean, no matter where you buy shower curtains, there are always 12 slots for the rings. And, no matter where you buy the shower-curtain rings, there are always 12 rings to fit in each of the 12 shower-curtain slots. Now these are the type of complementary businesses that actually has the consumer in mind. If shower curtain makers and shower-curtain ring makers can work in tandem, then surely a lot of other businesses could do the same. Dontcha think?