Well, Kate herself jokes about all folk songs being miserable, but I don't think that it is actually true of the English tradition. Such certainly exist, but alongside bucolic drinking songs, pastoral delights and sweet love songs. They may have the sailor going away, but back he comes. (With his broken ring on a bit of string...)

It was pointed out that English night visiting songs have happy endings, whereas the Scottish ones end in death, murder, drownings and the destruction of families... A gross simplification I'm sure, but maybe you've been listening to the Scottish songs Kate sings?

There are of course the sad songs about industrial working conditions, but many of those have been played up (or written) by the left-wing side of the folk movement. I'm certainly not knocking them, but when you're pressing for change you aren't going to play up the sunny side of life. Even when your predecessors did - to name but one example, Tommy Armstrong wrote his happy bouncy songs too.