There are costs associated with keeping boats moored at a marina just like there are costs associated with occupying a home.
For hundreds of people living in shelters like Rock Bay Landing and Our Place, they have zero costs for a home. Plus they get free meals. Plus we pay staff and operating costs at those places through taxes, and for many of their guests, we also pay for their daily methadone (that's hundreds of dollars a month each). Then some of them supplement their income by braking into homes and cars.
Those people require way more resources than the handful of people living in a few boats on the Gorge.