Dynymoor
I think it relates directly to how it is used and cared for.
I have a Creatures of Leisure 10' coil that I use on my 12'6" for ocean paddling, it has never been hammered. 2 years.
10' balin I use on my 9'6" All Wave and my 9'1" longboard used regularly and is five years old.
8' Balin use on my 8' gun 8 years old and no signs of wear.
I wash them thoroughly in fresh water after each use and make sure they are dry before they go in my surf box.
Never have wrapped them around my fins. I believe this is a big no no.
I reckon if you buy good quality and look after it they should last a few years at least.
Cheers. ET.