The reason dates back to the 2009 deal under which the port company sold Queens Wharf to the Government and the Auckland Regional Council for $40 million, the cost split evenly. The politicians agreed to build a cruise-ship terminal at no cost to Ports of Auckland.
The company, in return, would allow public access to the wharf as long as it did not affect cruise-ship activities, and look after maintenance and dredging.
This seems to have been a bargain for Ports of Auckland. Despite the inadequacies of the Princes Wharf terminal and the increasing number of cruise ships, it had not invested in a new facility.
Presumably, it always hoped public funding would provide one.
Now, there seems no way for Mr Brown to renege on the deal. He must, however, try to lever as much as possible from the port company in terms of spending.
Ports of Auckland now says it will pay the operating costs for the terminal when it is being used as a cruise-ship base, and spend "several million dollars" on a permanent gangway.
That aside, ratepayers' only succour lies in the economic benefit to the region of the 150,000-plus passengers who will pass through the terminal each year.
This means the mayor must pay particular attention to public access, the most important side of the deal from the regional council's perspective.
On no account must people be prohibited for no good reason. It should be remembered that the attractiveness of a public open space on Queens Wharf was, in fact, one of Mr Brown's main reasons for favouring Captain Cook for the terminal.
Ports of Auckland says the Queens Wharf terminal would be required by it for only about 100 days a year. For the bulk of the year, it would revert to public use.
Given that, it is important public events and entertainment are accorded a strong priority in the terminal design.
Making "modest, medium-term improvements" to Shed 10 is the right decision.
Cruise ships do not need elaborate embarkation amenities. Many ports do without them. Two factors are now paramount. The cost to ratepayers must be constrained as far as possible, and public access to what is limited space on the Auckland waterfront must be guaranteed as far as possible.