I reckon the CRT have spotted the increasing use of their canals as places for people to live.
Obviously it is a Good Thing to have people living on boats but if it is too cheap it can cause bias problems.
I think this will have been modelled and looked at and the increases, whatever they turn out to be, may be part of a strategy to manage the situation going forwards. There are new people on boats all the time and bearing in mind what living on a boat entails it could get dodgy it it got too popular.