I believe they do it because:
1. They know there are people that don't care and will buy it either way.
2. I think it nets them the biggest money return in the long run.
I mean think about it, let's say it costs hypothetically 2 dollars per person to download the file from there server. If it's priced at $5 and 100 people download they make 500 dollars, but lose 200 dollars. So it's only a 300 dollar profit. Now if 50 people buy it at 15 dollars they make 750, pay 100 servers and see a profit of $650 dollars.
and 3. They are just greedy bastards. Think about it, if you buy a Rockstar DLC at 30 dollars(which is only 15 more dollars) you get five to six times the content.
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