I looked around real quick. Castrol Edge 0w40, Pennzoil 0w40 from various sources are all about that same ~$25-30 USD range.
I would guess their blending costs are all similar. And similar to mine. As, at least with Castrol and Shell they use third party blenders for everything.
So the margin just isn’t there on 0w40 compared to your 0w20 / 5w20 / 5w30 full synthetics.
I also know what Havoline 0w40 is at the wholesale level, to compare it against. And sure my pricing on Havoline may not be the same as Walmarts, for comparison sake. So I’m going to say it’s just a lower margin product.