> I get the nostalgic aspect.

While you may understand the nostalgic aspect from a logical level, I don't think you understand it beyond that. This next line:

> But it's not like there aren't a zillion from-scratch brownie recipes to choose from.

To me anyways really indicates that. I know there are a zillion from-scratch recipes online and in books and in other media. That isn't the point.

> If throwing away some extra premix destroys the pleasure, then that's a low bar.

Once again, I think you are totally missing the point. I think this captures why it's a big deal: https://www.youtube.com/watch?v=3D8TEJtQRhw Betty Crocker is effectively doing that.

Without understanding it at more of emotional level, I can see why this doesn't resonate with you. Unfortunately, that also means it is unlikely that you will able to understand why it is a big deal and why other folks are arguing with you the way they are.