Pattern companies don't make needles, so that's not a really strong arguement. It's pretty simple really. Needles with really flexible cords are fairly recent, maybe the last 5 years. The Magic Loop booklet which popularized the method was published only 10 years ago, even though some of us had been doing it years before that. We just never thought about printing a book about it.
Dpns have been around forever and were what you used to make socks and hats with, shorter needles have only become readily available in the last 10 years too. So ML is a more recent method of knitting and not a lot of older knitters or patterns will use it, only newer ones. And it is a very personsal preference, both by designers and knitters. Some hate ML and love dpns, some the other way, so there's no real conspiracy by anyone.
sue- knitting heretic