So the more casual player can test the raids out, see the mechanics, get familiar with them and maybe make a transition to normal mode. Literally nothing would change for the crowd already doing normal modes. They wouldn't lose anything. Their loot wouldn't be taken away. Their "prestige" would remain. The only valid argument to be made here is that designing an easy mode would take resources away from other game modes. Other than that, there are absolutely no downsides in enabling content to much wider audience.