Huh, I was thinking that the natural fiber ropes actually held up to sun exposure better than synthetics. Much like a cotton duck fabric tent (thinking of a Scout summer camp wall tent) lasts much longer than a nylon or polyester tent.

Most of the long-term tie-downs used at summer camps (wall tents, axe yards) are done with natural ropes and last for a long time (assuming Scouts don't damage them).

Natural ropes are certainly more prone to rot though.

My other experience with natural fiber rope is that once it gets wet and then dries, it shrinks very tight, especially with well done lashings. Sometimes I've needed to cut the rope to disassemble lashing projects that have gotten wet and then dried.