There was no kudos in preservation in those days, let alone any political mileage in it.
The Americans had sent a man into space, were building 16-lane highways and 50+ storey skyscrapers; and the 'cool, with-it' British wannabees were going to copy that technology for the space-age society, not waste their time on preserving old Victorian technology.
BR management seemed to know what they wanted - a sleek and fast railway to compete with the airlines - but did not really have the technology to be able to get it precisely when they wanted it. Hence the apparent financial incompetence of chopping and changing with different ideas about traction along the lines of "Oooh, they look modern, lets order lots of those" followed a little later by "Oooh, those newer ones are even better, lets order lots of those, and scrap the previous ones"... and repeat.