There are arguments for the project:
1) The only way to get to Ketchikan's airport is by ferry, which can be unreliable. For example, according to the
Environmental Impact Statement for the bridge, if there is a medical emergency, the ferry is taken out of regular service to bring the patient to the airport. Regular passengers then miss their flights.
2) Ketchikan itself has little flat land to grow. Everyone thinks of Alaska a wide open, but Southeast Alaska is different. Ketchikan is built on the side of a hill on an island along the famous Inside Passage. Gravina and Pennock Islands are much flatter and undeveloped. There's room for industrial development.
3) The cost of the bridge was increased due to the need to make sure cruise ships could float under the span. Cruise ship traffic drives Ketchikan's economy. Cheaper alternatives that were studied were either too low or too close to the city's main seaplane base. Seaplanes connect remote Southeast Alaskan villages to the rest of the world.
4) They studied other alternatives, including building more ferries and a tunnel. The ferry infrastructure would be cheaper to set up but much more costly to maintain. The tunnel was even more expensive than the bridge.
I'm not saying the cost is justified. But to describe it as just a bridge linking an island of 50 people to Ketchikan is a bit misleading.
By the way, there are actually two bridges to "nowhere" here - one 200-foot high bridge from Ketchikan to Pennock Island, and another 120-foot high bridge from Pennock Island to Gravina Island. Very few people currently live on Pennock Island.
I see the article also fails to mention that the bridges and other earmarked projects required Alaska to give up 600 million in non-earmarked funds. In other words, the funding for the majority cost of these bridges came from Alaska's general transportation funds.