Soft hanks and Soft shackles

[petermat]

Earlier today I had never heard of, let alone seen a "soft shackle", so please bear with me. I have looked at several threads here, and also several suppliers sites, and I am still very unclear. (I have looked at Jacks photos.) OK I see there is a stopper knot at one end and what looks like an eye splice at the other end. The stopper knot fits (just) through the eye. So why does the stopper knot not come back out of the eye, particularly in a flogging (jib) situation? And why are they so expensive - the cheapest I found was $30! For a few inches of line!