Why wouldn't they? I'd expect a demo to be representative of the final product. If it's not then a demo is simply useless, or worse, deceptive, as you can't base a buying decision on it. Especially for this game, which is a looter shooter after all, messing with the balance and economy is a pretty big deal being that's what those games are built around.
But why should the balance and economy matter in the demo? That's the least important thing. Gameplay and presentation matter nothing else. Hell Destiny beta , Division beta had different economy than retail,... and yet both convinced people based on that, why can't Anthem be given that chance?