For the vendors that don't sponsor, you don't know whether the amount they save goes into a higher quality product. Maybe it did, maybe it didn't.
But for the vendors that DO sponsor, you definetly know that the money didn't go into a higher quality product.
Some eCommerce companies who are agressively using Google/FB/Social will spend 30%+ of their revenue just on online/influencer advertising (based on companies I have worked with).