'what was it about 'old' labour that caused 'the people' to lose faith/support in it?'
The times, but the times are a-changing. The pubblic mood is swinging and has swung against the Establishment which is why we beat them in Brexit.
'What has changed, and what evidence is there that repeating history will be different this time?'
Things have got worse for millions of people. There is less social mobility than in the 1970s, we had a Cabinet stuffed full of Old Etonians, people can't afford to buy homes in huge numbers as house prices rise and there is a lack of new builds. There is a shortage of council homes and higher rents as well as much greater immigration and pressure on services. Jobs are now less secure as Blair failed to reverse union restrictions and employers now offer zero-hour contracts etc. Free university tuition is gone and people are clocking up large debts in an attempt to better themselves by educating themselves.
The rich and fat cats have got richer, the 1%'s wealth has increased while the people have had to suffer austerity to pay the bankers and fat cats back who caused the financial crash from which the entire world has still not fully recovered after 8 years where interest rates are at zero and are going negative in some countries.
That explains the rise of Corbyn and the Corbynistas.