Destiny? Are you kidding me?
This is not a lottery, this is businness and cannot rely on just fate by design. It's just broken this way.
Would you accept to get to the last boss on an OP or HM FP and have a chance roll to find the door open or closed and actually be able to play it? This is exactly the same.
I would not compare it like that, it's more like everyone get to kill the boss if they want to and have the time but it's totaly random what it drops, you can't chose that either.