The whole "scandal" thing is generally pushed just by streetcar buffs. The fact is that, worldwide, city tramways disappeared in the 1950s (in particular), once buses had become reliable and cheap (and notably faster as well), cars had become widespread, and (point often missed) the capital plant of the systems became life-expired, because they had pretty much all started together, in the 1900-1920 period. The built layouts of cities and suburbia, driven to quite an extent by buses and cars, changed in a way that tramways could not keep up.
Sure there were a few exceptions. But this was the general trend. City tramways also disappeared at this time in MOST of the major urban areas of Britain, France, Australia, etc. They can't all have been conspired against by National City Lines.