bill, it just does. You attach the tow bar on two points, if you just attach it in the center with a foot between the 2 attaching point, then yes, it'll wander.
If you DO lock the wheel, when you turn, the towed vehicle will go straight and push you into a jack knife spin out.
Ask me how I know. I was able to pull out of it though.
We had this cat when i was in the army, insisted on needing some one to steer the 2 1/2 ton cargo truck I was towing... even though I showed him in the manuals where he was wrong, he out ranked me and he couldn't be told otherwise... so i said to hell with it and started towing the tard. He tried to steer around a corner, bound up the tow bar, snapped it, and the steering wheek kicked back as the tow bar snapped, and broke his arm and about 5 bones in his hand. The dumb ass ended up in the ditch.
So me, being the smart allek punk that i am, pulled out the book, and showed him where the regulation says no one is to ride in a vehicle being towed.
He wasn't amused.