It's not that they always don't carry it, and I should note that Walmart's online selection contains practically every product possible, and is not necessarily analogous to what you can find on the shelves at your local store (that's why I said
go to your Walmart).
Even if a healthy alternative is on the shelves at your local Walmart, and it sometimes is, virtually all of the shoppers are going to come back with an unhealthy option thinking it's healthy. The one or maybe two items that are actually healthy (and by "actually healthy", I just mean real food; something you can make from a plant or animal without a chemist's involvement) have to be picked out from dozens of nearly-identical SKUs that are deceptively labeled.
Try this on someone who doesn't know you're going to try it on them: check the ingredients and values on someone's healthy food item that they got at a mainstream grocer (Target is almost the same as Walmart, they just have a more prominent nut section) and see how much sweetener was added to it. My health-conscious buddies usually find out that their premium "super-healthy" green band 100% whole grain wheat bread has added sugar.
I actually have bought real maple syrup at Walmart. It was tucked in the very top corner of the shelf and there were only three units stocked. By contrast, there was a whole section of thickened, dyed sugar water syrup on the wall, probably 25 SKUs. Again, the issue is not that it's hypothetically impossible, the issue is that 99.9% of the patrons, even those who are intentionally trying to buy a healthy option, are not going to be able to do it successfully. There's a reason for that, and that reason is that the grocer, the distributor, the manufacturer, and all the rest of the way up the supply chain, they don't want you to be able to buy healthier, because access to more filling, low calorie options means not only that you'll be healthier, but that ultimately you'll buy a lot less food.