Because both sides are addicted to the idea that if their guy did it it must be OK. Remember when all that ammo was being bought by random federal agencies under Obama, the right was freaking out. Trump deploys the random agencies to quell the riots, probably with some of that ammo in their guns, but the right is OK with it. Not our guy vs our guy.
You are confusing conservatives with Democrats and leftists, and raising a bad straw man argument. Please think about the situation more carefully.