Contest modifier offers an incredibly unique and difficult challenge that's not present anywhere else in the game. It can give people the same feel of the day 1 raid even if they weren't able to make it there on launch. Adding the option could also possibly provide an extra piece a loot per encounter completion or triumphs as incentive. The raid becomes a cakewalk in terms of difficulty in comparison after day 1 and I believe this is a change many people currently want and would help keep raids interesting and relevant when played repeatedly.