Me too! and that's partly what makes this a social interesting documentary! I have a few ideas ......
1. They enjoy making these videos so much that even when they haven't actually got anything to show, they'll do these to tide themselves over until the next parcel arrives (which in some cases can be hours, not days!)
2. They genuinely think they're helping out other members of the community by saving them the trouble of finding bargains
3. It generates thanks and praise
4. A bit of a stretch this one, but I do wonder whether they believe that someone in the business is watching and tallying up sales, seeing how many extra sales are being generated and eventually they'll be invited to Chiswick to receive an MBE for their services to shopping telly, then whisked off to America to meet the CEO, sent back home with a lifetime supply of polyester and HS candles ( and a fire hazard warning), given their own show on the main channel called "Heads up" - an hour's worth of rambling about various products that can be bought elsewhere for a quarter of the price
5. Mainly, I'm as baffled as you are - It's a pointless excercise!