Because we spend the exact same time earning strange coins as you do grinding. But can you say you earned something when it is all up to luck if it drops? It's rng if a mob drops an engram, its rng what the cryptarch gives you from the engram, it's rng when you get end mission rewards. So how is being lucky better then earning coins and buying stuff? I was killing mobs waiting for a daily event to pop up, I killed maybe 6 mobs and a legendary engram dropped from it, I brought it to the cryptarch and got the Cryptic Dragon scout rifle. Did I earn that legendary scout rifle, hell no because it dropped after I killed 6 mobs, it was just all luck that it dropped.