The boats lots of people complain about who sit on short-term moorings (or the same place on the towpath) for weeks/months or even years, and only shuffle round a tiny area if they move at all. Maybe they're NBTA members/supporters or not, but if not their aims seem rather similar, which is to bend or break the CC rules as far as possible. "Parasitic" seems the right term to me -- do you have a better one?
To see this you need to observe one area repeatedly over a longish period of time, which obviously I didn't do on a one-way trip of a few days -- though I had suspicions about boats on visitor moorings in several places with no signs of life, this isn't proof. However many posters on here have mentioned such unmoving boats, again based on repeated sightings over a considerable time.
But I do see this all the time (over repeated sightings) on the canals here in West London, and there are *plenty* of them... 😉