Two other reasons I can think of;
First the union movement got into such disrepute by the late 1970's that when a certain lady P.M. decided to not just neuter but dismember the body, no one really cared. Which means that all unions find it harder to show any muscle these days
Secondly, although our income may not be great it is still above average for the UK. So compared to our friends and relatives most of us are better off. That brings a kind of complacency. I am especially sad that we even treat the next generation of pilots the same way. How else do you explain the proliferation of 'B' scales and the constant erosion of pension and other benefits for new joiners. We shouldn't put up with it but our own comfort makes us lazy and complacent.
Sad but there it is.
Right, I'm off to renew my Labour Party subsription..... Doh!