Probably 'cause some guy invented them.

[ There's a smirk shot in her direction before he looks back to what he's doing. ]

Nah, I don't rightly know why. Never thought to ask. And it gets stronger the more you stake it, but you're right that on loose ground it's never gonna work right.

[ He loops a guy line at the top of the tent pole and stakes it into the ground before coming over to her end, now that his is up. ]

So you stake it at an angle facing in towards the tent. More tension that way.