Except beyond a certain point it doesn't make it more expensive. Crack ROT13 or BD+ or AACS or whatever and what you have at the end is the plaintext, that then gets distributed around.

It makes it harder for a few people that crack it for fun, profit, kudos, whatever it is, but then it's exactly the same.

There is a reason for it, but mostly the reason is pretty misguided, and it absolutely does make the experience of the paying customer worse than that of the pirate.