I'll tell you why, Bungie doesn't know how to make a strike boss include good mechanics such as jumping on walls and being a hard target to get precision damage on. Instead they give us Bullet Sponges like the Archon Priest, Sekrion, Valus, Sepiks, Taniks, Walker Tanks, etc. that take roughly 1-10 minutes to take down with the right set-up excluding Ghorn and Bhammer. Then they see how well these weapons work against their shitty designed bosses and think "well we can't change how you guys fight them so we'll just cripple the weapons you use instead and if that sound good enough we'll also make sure your good legendaries don't do jackshit in the Taken King so you can start all over and use weapons that will have really good perks like Shank Burn."