I think that one of the reasons that Walmart can sell their fabric for a low price is the volumes they order. Think about how many Walmarts are in the US.
However, we did have a speaker at our guild meeting years ago that told us about fabric runs. She said that runs are made on lower quality fabric to test the pattern. If you have ever seen a flat fold fabric with the design printed a little off, it is probably one.
I have fabric that has been stored the same place and way, but some of the older fabric from Hancocks is fading away. I, also, have a quilt made from a football field panel that I purchased at Hancocks for $1 and it is fine after many years. Not all fabric is equal.
That being said, I buy what I like. For many years, there were no quilt shops near me. I do buy quilt shop fabric today, but Walmart had Spiderman fabric and my DGS loves his Spiderman quilt.