I used to agree with that sentiment... we've used to build so many of our ferry boats, so why give money and jobs to other places so they can build boats for us?
However, if you pass by the North Van waterfront, the answer becomes painfully clear... the former shipyards that used to build the mightiest ferries in the fleet are all gone. I guess many of them went under in the 1980s and 1990s, with their sites now occupied by new apartments. Only a few companies (like Vancouver Drydock) exist and they are generally specialized in repairing ships and building smaller craft... not the larger ships of yesterday. A similar state of affairs is also present in the Victoria Shipyards.
One only has to look at the Island Sky (built 2008) to see the problems with building locally nowadays. It wasn't a big ship by any standards but it still ran over budget (fortunately covered by the contractors) and had numerous issues that delayed its delivery
(link) and entry into service. Compare that to the contract for the four newest large ships in the fleet. All were built on time and on budget with few issues whatsoever.
Unless there is a strong interest by British Columbians and the government to re-establish the ship-building industry here with a skilled technical workforce that focuses on quality and workmanship while sticking to deadlines, foreign purchases are generally the way to go in the future for most ships of BC Ferries. It sounds sad, but times and situations have changed... and we can't always stick with the old mentality.
PS: Rumour has it from West Coast Ferries Forum
(link) right now that BC Ferries might buy some fresh new smaller ferries from Europe from shipping lines that have hit hard times over there while construction was underway.