Since raiding at 60 was super easy throughout Cata and onwards, Thirk had the genius idea to start this project with other people.
It took off really slowly, but eventually happened. In my opinion, the reason for 50 is for the insane challenge. Progressing through level 60 raids as a level 50 gave (to some) the nostalgia of doing vanilla raids with the difficulty they were intended to have. There is practically no room for mistakes. You need to kill the bosses with the right mechanics (mechanics of vanilla fights are almost long lost).
However, I've got no idea the current state of 50s right now. As a healer, I never really looked into the hit rating for 50s but I know the DPS had to have A LOT of it. Now that its removed, I have no idea if its still doable! :/