It decrease them. Eventually, it's either you make more by selling at higher PEGI, or less. Mortal Kombat sells more because people want the gore, it would sell less otherwise.high ratings don't stop sales from most of the best selling games of all time outside of games that come pre packaged with consoles or are Nintendo originals.
I'm sure call of duty is so sad it didn't get a child rating to sell more copies. so is mortal kombat. etc
Total war sells more by being a lower PEGI, because people don't care that much about gore, and 12 years old kid's mum apparently do.