Because it doesn't have the approvals? The approvals guarantee a minimum level of performance. Yes, there are products that go above and beyond that, but you aren't finding them branded Supertech or Amazon Basics and they cost considerably more than formally approved products.
This is the "pile of failed engines" fallacy. An inferior oil typically won't cause catastrophic failure. What will happen is more piston ring deposits than allowed by some of the OE tests, more wear than is allowed in some of these OE tests...etc. Typically just poorer performance. If you don't own your vehicles long term, it's likely of no real consequence; it's certainly of no immediate consequence, but that doesn't mean it's not of detriment.
Bad analogy, those are two different drugs (Aspirin - acetylsalicylic acid and Tylenol - acetaminophen). Regardless of whose name is on the bottle, chemically, the store brands and while box products are the same as the brand names (though there is some question on QC on some of the white box substitutes regardless of them being approved products). This is quite dissimilar to engine oils when discussing big brand names, like Mobil 1, with store brands, like Supertech, which can have wildly different formulations.
A better analogy might be to compare Chinese surplus ammo to various qualities of boxed ammo. Or perhaps comparing McDonalds to a 3 or 4 star restaurant. Yeah, they are both food, but that's about where the comparison ends. You could extend that particular analogy to the movie "Supersize me" as to the results of doing the McDonalds diet, which likely correlates reasonably well with using a subpar lubricant in an application that calls for a specific approval.