A restaurant has a fixed number of reservations possible. How do you suggest allocating them when demand exceeds supply? One way or another, some will not be able to get a reservation.
> There are many things that are beyond supply and demand: love, sex, children.
Those are most definitely connected to supply and demand.
High status men get high status women, and vice versa. What do you think drives the price of a hoe? And how many children one has is often the result of willingness to pay for them.
> Why should restaurant reservations be any different?