Check this out:

http://www.briontoss.com/education/archive/miscfall01.htm

Seems all that nasty stretch comes from the braiding or even heavy twisting used on some types of lines. But these high modulus fibers do not like repeated bending, presumably even within their elastic potential. Thus braid or heavy twist is the only option for a beach cat that's going to be set up and taken down repeatedly. Otherwise the rope strength degrades.
I guess from an engineer's perspective, beach cats do not have any 'standing' rigging; it's ALL running.

Learn something new every day!

Jimbo