Perhaps where the market thought model breaks down is that in a marketplace, the value of the product offered is compared against the price and the transaction

Perhaps where the market thought model breaks down is that in a marketplace, the value of the product offered is compared against the price and the transaction goes forward or does not. Friendship requires some sustained investment and so might be modelled more like a chemical reaction: high activation energy to gain new friends with comparatively lesser energy going into the interaction once the friendship has been established. With this model, it makes sense that individuals would seek to maintain existing friendship instead of acquiring new ones because the energy expenditure is much lower in the former than the latter.