The only use case that makes sense is I can see it being used for is reorders of brand-name consumables you've already vetted. But even when you trust you're getting a product actually made by Tide (or whomever), its unclear you're getting the exact match as a previous purchase - the brand may have decided to repackage it into something 6 ounces less than before. This happens a lot. Prices also tend to fluctuate quite a bit, enough that occasionally you'll get a price way outside normal range and would benefit from looking at other brands.
Lots of room for error, and voice as a channel is too narrow to deliver an efficient experience that corrects for these issues. These are fixable by Amazon, but judging by what little policing there is on the authenticity of items, I doubt it'll happen anytime soon.