I would have thought the line would just wrap around the agitator of a top loader and never really agitate. Worse, I would expect them to tangle all up around it. In a front loader, they continually tumble. I bet you essentially just soaked them.I tried washing my jib sheets in a mesh bag in my top-loading washer, and they came out just as dirty as they went in!
I can see how a front-loader might do a much better job.