Fair Play Contracting - Why are some Contractors treating their Supply Chain unfairly?

It amazes me that still, after some 25 years plus of reviewing Sub-Contracts, that some Contractors still insist on grossly unfair contract terms and conditions and rather than, when the Sub-Contractor puts forward reasonable amendments, the Contractor response is "No, take our conditions or you do not get the job".

This is so short sighted; Contractors are in the majority of cases managers only without the Supply Chain but yet, some insist on notifications of delay and notices of loss and expense for example within 7 days of the event, failing which the Sub-Contractor lose their right to any additional time and cost for failure to do so. The Sub-Contractor then puts forward, for example, what I would say is a a reasonable amendment of 42 days and the answers is no.

I do understand that the Contractor has a duty upstream and they ought to have foresaw that a 7 day period is too tight, but still, the industry will not change and firms will never make good margins with this practice continuing; lets face it, most Contractors struggle to make 3% margin on their annual turnover but yet sub-contractors do make more than this overall, but the margin is still measly when compared to say, consultants and other firms in different industries.

Some Contractors who adopt this practice need to change and then change the Employers view so that all firms working in the industry can make a decent margin to re-invest in their business for health, safety, training, pay increases etc and distribute to shareholders.

Have you come across any similar practices by Contractors and if so, how have you dealt with it?