Me too. That’s where I get oils with demanding manufacturer approvals such as VW 504 00. Same price as other synthetic oils and Walmart is the lowest.Cost and convenience, and some are worried it might be a warranty issue. I don't have that problem since I stopped buying new cars long ago. Cost and convenience means I purchase most of my oil and filters from Walmart, so what is available there heavily influences what I buy.
I did buy filters there in the past but obviously that’s changed. I get them at O’Reilly these days.
I have no concerns about warranty. Nowhere in my owners manual does it say I’m restricted to using what they recommend to preserve my warranty. But like you, everything’s out of warranty now. I drive things to the very end so superior protection and longevity is important to me.