Volume,
There isn't enough money to buy the fuel to move an aircraft with the weight per seat and specific fuel consumption of the 707, and it couldn't make a third of the range of a 787.
The lifetime of the new devices is also much better. Fasteners aren't just wrenched and hammered in, their performance is dramatically better.
Brunel's drawing office would make a very very uncompetitive airliner in 2013.
Back in the 1960/70s also consider aircraft losses. That engineering/flying system delivered aircraft into service aboard which passengers and crew were lost about one hundred times more often that in today's in terms of crashes per passenger-km.
There is an issue with the loss of manual skill and intuition in engineers, but the best ones are just as good as the old hands, and overall products produced are dramatically better.
Compare a regular Ford now vs a Rolls-Royce Silver Wotsit in 1970? Which performs better? Is more comfortable? Needs servicing more often?