I’m pretty sure capitalistic supply and demand comes into play here too. If there was less demand the cost would be lower. Apparently there is sufficient demand to maintain the current cost structure. Plain and simple.
OK, how much to ride the ferry as a walk-on passenger?
I took my 1970 Oldsmobile Vista Cruiser and 4 people over to Vancouver Island (Victoria, B.C.) about 15 years ago. We spent one week there. Ferrying the Oldsmobile and ourselves cost less then if we were to walk-on the ferry and rent a car. I did not figure out how much it would have cost to just park the Vista Cruiser in Seattle or Bremerton . The budget was already blown with the car rental. BTW we went from Seattle to Victoria/Vancouver Island to Bremerton.
Fascinating. If you factor in the 54% government subsidy for the Seattle Ferry, and increase the fee by the relative difference in mileage (24 miles versus 16), you end up that the Seattle Ferry “should” cost $94, if you were paying the cost upfront without government subsidies, and it had to go 24 miles.
Apparently, the Vancouver -> Victoria Ferry operators are charging a fair price.
So, does that boil down to The State of Washington being more socialist, and BC being more market-governed? 
Except your logic is very wrong.
Gas and maybe maintainance can be scaled that way but spending $100,000 on a ferry that goes 6 miles does not mean I have to spend $150,000 for a ferry that goes 9 miles and pay for an 8 hour day should be the same no matter how far the ferry travels or how many runs it makes in that 8 hours.
Don’t forget that the ferry doesn’t run from Vancouver to Victoria. As a walk-on, you have to take a bus from Vancouver to the ferry terminal, and then after the transit you have to take a bus from the other terminal to downtown Victoria.
15/person. The Anacortes ferry to Vancouver Island is ~90 for three people and a car so that’s an option as well.
It’s been a few years since I’ve gone to Victoria or Nanaimo - but they seem less like commuter ferries than the Seattle-Bremerton ferry is.
The total pay ‘no matter how many runs it makes in that 8 hours’ isn’t the factor that’s most relevant to the passenger cost, it seems to me. If the average pay per trip is more, then that’s a higher labour cost that is eventually passed on to all the passengers on the ferry for that trip.