If I understand correctly, one purpose is to encourage members to sign up for the silver or gold memberships in order to provide financial support to the site. A related purpose is based on the theory that those who pay membership fees and thereby support this site should be accorded some kind of incentive or benefit [other than the prize draws] -- something akin to the "user pays" principle. Offering free products or services, while a good thing for a consumer, does not make commercial sense.
As for a targeted market, I understand your point. You are correct, but those who cannot afford silver or gold status might not be able to afford to buy B&O or to pay the asking price or near asking price. Further, the official B&O site offers free listings. Although e-Bay charges fees, dedicated B&O enthusiasts often will trawl the B&O auction items. So there are alternatives enthusiast sites to sell or buy.
As for "bargains", chances are those bargains will not be found on enthusiasts' sites as enthusiasts will generally have a better idea of the value or worth of an item than someone at a car boot sale. You do get what you pay for. Buying from an enthusiast generally will ensure the sale item has been properly cared for and not abused. That cannot be guaranteed purchasing, say for example, a second-hand shop which treats the B&O like a piece of junk -- I have seen one MX6000 sitting under and behind piles of other used electronics getting all scratched up and dusty while the Beo4 was thrown into a drawer jumbled with all the other remotes.
If I am incorrect, I am sure a moderator or Lee will provide you with a better answer.