I just like the word.
But also I read a book as a child and there was a house in it called Seldom End.
When was thinking what to call myself it just popped into my head. Being as there was nothing else in there there wasn't much of a contest.
The other reason it fits is because I'm given to fits of not writing anything at all and fits of writing manically for days on end. Unpredictable and seldom. Am also given to fits of disappearing.
Judge for yourself how well it suits.