Why is there no "mother of all websites" for retailed goods? It seems like it would be a fairly simple thing to do. Retailers batch-submit the goods they have for sale to a given website. The website tracks price, qty in stock, what the item is, and useful specifications, matching up items as appropriate via UPC barcodes or whatever other unique identifiers they might have.
I suppose what I am picturing is sort of like Google Shopping, but with categorized items (enabling browsing by category) that are retailer-pushed rather than bot-scraped. Sort of like the eBay of retailing. eBay + Google Shopping, then, but without multiple listings per item. Amazon sort of has the right idea, but everything goes through them, so if a vendor isn't set up to sell through Amazon, you don't see their goods.
As a consumer, I would love to have such a website with comprehensive, up-to-date information on who to buy from and what the best prices are. Why hasn't a project like this been undertaken?
Because directories are inefficient and silly, due to the volume of data that is largely irrelevant to an individual user. That's why Yahoo, which began as simply a directory of sites, got trumped by Google, which crawls and indexes.
Just use google shopping. It's a far improved version of what you're looking for.
shopping.google.com