I can't speak for 1974 Nicro, because I didn't come into the industry until the mid 80s. Still nearly 30 years though.
My read would be this.
Firstly, the total amount of technical knowledge in those days was miles less than it is now. Just take filling a tank or cistern - there were maybe 5 or 6 common ballvalve types, and another 3 or 4 uncommon ones. Everything was manufactured to be repaired, reseated, re-washered etc. Back in those days, a ballvalve cost about the same as an hours labour, so there was an incentive to repair it. Now there are about 200 different fill valves on the market, its impossible to keep track of how they all work, and most were not manufactured to be maintained. Even if they were, you couldnt carry all the spares in a juggernaut, never mind a van. A replacement costs about the same as 10 minutes labour. So they get replaced, not repaired.
On the other hand, the degree of craft skill required then was way higher than it is now. Whether it was wiping a lead joint, caulking cast iron soil, threading barrel - all that got killed off with timesaver this, plastic that, and pushfit the other. This tempts people to believe that "this plumbing lark is easy". And if you don't care how neat it looks, it pretty much is easy. Until something goes wrong.
Back in the day, if you had a good understanding of first principles, and well practiced craft skills, there was nothing that could go wrong that you couldnt fix. Nowadays, that simply isnt the case. Why isnt the boiler firing? Back then, it was either the thermocouple or the gas-valve, or no money in the meter. Now it is as likely to be that the wi-fi is down, so the app can't talk to the smart controller.
The old uns think the young uns are idiots because they can't re-washer a portsmouth ballvalve with their eyes closed. The young uns think the old uns are idiots because they can't install an app for the phone to control the heating. Who's the idiot?
In terms of attitude, I think it has polarised. We used to open at 8 am, and if I turned up to work at ten to eight, there would be a couple of vans waiting outside. Now we open at 7 am, and there are often 6 or 7 vans waiting at twenty to 7. Equally, there are more really idle barstewards.
Life moves on...