Actually, the reverse happens far more often. If a company manages to insert themselves between you and your users, they can then work their way down the value chain and replace you as a supplier. It works both ways and typically the company with the direct consumer relationship has the advantage.
Costco distributes food under the "Kirkland Signature" brand, competing with its own suppliers.
Uber was started by using a towncar service and getting cars dispatched. They now hire their own drivers directly.
Old fashioned steel companies were famous for owning the entire supply chain, all the way from the coal and iron mines and the rail roads through the steel factories.
Google is (attempting) this move by creating a review service to eat Yelp's lunch and displace them as a supplier of reviews to people searching Google.
Netflix creates House of Cards to compete with its own suppliers of movies.
In terms of supermarket chains I understood it to be whitelabelled - i.e. that primarily they have their own-brand goods manufactured at a factory that already produces the goods sold under other brands. So, for example Tesco have a "wheat biscuit" product physically identical to Weetabix and indeed it's made in the same factory. Do Supermarkets really run their own factories for many/most/all goods sold under their brand?
I worked in the past at a supplier that labelled goods on the same packing line for different grocery retailers (QC and the label being the only differentiators).
