I figured it out myself a long time ago; I noticed that the BO looks like a chain st and the it's similar to crochet. I found that I definitely need to knit the last row on a larger needle when I use the crochet hook, or the BO will be too tight. It's good when you have about 300 sts to BO on a shawl.
I've noticed that the BO looks like crochet, and if I'd thought of it, maybe I could have figured this out too. But it never occured to me. That could be a useful arrow in my quiver. Thanks for sharing that one.