You'd be surprised how hard it is to identify SHINE. In places like this, you'll probably find the fastest broadband available is actually ADSL2+ - which is highly susceptible to noise, and in some places in the UK the lines which run to peoples houses aren't even copper, they're ALU - which is obviously not ideal. Even the tiniest of things can have an enormous impact on line performance.

I worked at a UK ISP a couple years back and lets just say the 'monitoring' that ISPS have is extremely limited. Openreach (the company that manages the phone lines, which ISPs lease) almost certainly has more monitoring but the problem is the customer calls the ISP, and the ISP then tells Openreach - which means there's a fairly huge disconnect between the customer and the engineers fixing the line.