Because they are evil robbing theves, who want to extract the most possible cash out of their poor old boaters.
Personally, I think a residential licence sounds like a total disaster, given that most livaboards are on moorings that don't actually have planning permission. I can see being caught between the devil and the deep blue sea on this one - either I have to tell BW I don't live on my boat, or have the council find out that I do. Lo and behold, I end up joining the ranks of the CC'ers promptly, and find myself working round the Cheshire ring on a full time basis.