Not because I don't know what to say, but because I have so much to say that I can't seem to condense it into a coherent train of thought, much less essay.
But that's just one of my problems.
What I should have been doing, and will do for the next two papers like this, is writing a synopsis for each book as we cover it. -- I've taken great notes, I just need more of a coherent scheme that I can put interrelated themes together so that I don't have to work so hard to remember what we talked about four weeks ago in class.
So, I'll get better. I'll do it better next time. I'll write it better as I go along.
Go forth and write!