I know that ferries to the mainland used Sturdies and those to Swartz Bay used Montague. Sturdies Bay, being more open, was perhaps seen as more difficult to get in and out of in rough weather for the smaller open car deck ferries running to and from Swartz. But my #1 suggestion as to why was to minimize traffic through Active Pass.
Montague Harbour predates BC Ferries. Before there were direct connections to Tsawwassen there were only ferries to Swartz Bay. For ferries serving the Gulf islands out of Swartz Bay Montague Harbour would seem a more logical choice then Sturdies.
I assume the closing of the Montague Terminal was done to save money. However, today all ferries serving Galiano have to transit Active Pass. The extra costs in doing so must be less then the costs of running two terminals.
Salt Spring Is has three terminals. While Vesuvius terminal makes sense for the route to Crofton you have to wonder if they really need both Long Harbour and Fulford. For the same reason that they closed Montague would it not be less costly to run the Queen of Nanaimo out of Fulford, in spite of the somewhat longer distance involved?
According to a 1981 BCF publication titled "Ships And Terminals Information", which is available in the reference section of the Nanaimo Harbourfront library, which details capacity of various terminals at that time, Montague Harbour could accommodate up to PR class vessels, Sidney class only at high tide. One assumes the same might have been the case for Queen of the Islands, hence the decision to use Sturdies for route 9.
As for closing Montague, it is a similar distance from Village Bay to either terminal, but moving route 5 to Sturdies allowed for a greater range of vessels to operate on the route, vessels which were coming available to use there. That's my guess, anyway:)
Currently the Port Side wingwall has been replaced. The Starboard side wingwall is still in the process of being replaced. Currently the ship pushes up against one piling on that side which makes for some interesting landings since it obviously doesn't have much give compared to a wingwall. This was the case while the Port Side wingwall was being replaced as well.
A look at the barge activity going on next to the berth. You can see the parts for the new wingwall being stored here.