Also optimization happens between a minimum and a maximum. If Bethesda defines that the game should have a certain minimal visual quality (texture and model resolution, render distance, etc), that will lead to the minimum that hardware has to offer to handle it.

What modders so far did, was to lower the minimum further (for example by replacing textures with lower resolutions). That's a good way to make it run on older hardware, but it's no optimization Bethesda would or should do, because that's not what they envisioned for their game.