Y'know, that's a good question. I'm not sure I know the answer. My guess is it's largely for historical reasons. At the time most venues were organized PDF was

Y'know, that's a good question. I'm not sure I know the answer. My guess is it's largely for historical reasons. At the time most venues were organized PDF was probably the best (or only) mechanism for sharing documents for print distribution. But we think it's time to change that :).