Why have Schwalbe Nobby Nics got so weak sidewalls?

As good a morning as you can get in late November up in the Pentlands.

A terrific mornings riding today in the Pentlands spoilt only by my rear tyre, a Schwalbe Nobby Nic, having not one but two small splits appear on the sidewall. I'd read the reviews on these tyres and stupidly ignored the fact that about 75% of them considered the sidewalls to be very weak. Rather I was taken on by the fact that they were cheap and to be honest they are very good in every other respect. Probably as a front tyre they wont be so prone to splits (we'll see!) but as a rear they're, lets be honest, CRAP! Anyways I had been running it tubeless but had to stick a tube in it to complete the ride today. Apart from that distraction is was a great ride with over 32 miles covered and nearly 3500 feet of climbing, a good bit of training for January's Strathpuffer, but I doubt if the weather will be as agreeable then!