Answer :
Because it's their fireteam!!! If you don't like it join a different fireteam or create your own.
Don't sit there and argue or complain about their requirements, they are not going to change it because you don't like it.
My requirement on LFG for doing a raid is always a Grimoire requirement, if you don't have enough Grimoire don't sit there and argue with me or complain that it is a stupid requirements, just go and find a team that wants you.
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Yea i like when people have requirements, usually means they are tools and/or suck at the game and need to be carried. Have fun with your stuck up s00per 1337 fireteams breh! Ill be over here playing with no mic and chillen instead of worrying about how some random numbers represent me in an imaginary world