Most people just want to play with others who are like them. If someone has an hour or so to raid then they want to finish the whole thing which means finding people who have completed the raid already gives them the best chance. It is the second week so many people are trying to finish it for the first time and have already spent many hours with different groups with no success. Also, higher power level often means you can beat each encounter in less phases which makes it easier. So thats why people have those requirements.