It is because the pre-1950's generations are still considered by society to be the greatest generations. They are a hard-nosed, no-frills, people with traditional morals who tell it like it is. They won WWII and built the US into a super power and are considered to have established the gold standard in public policy. The era of the early and mid 1900's is also marked by extraordinary revolution from the telephone, automobile, airplane, radio, radar, computer, manufacturing, and medicine, which have only been refined and improved on today without fundamental revolution.
The list of achievements from the recent generations are comparably poor with some achievements in certain areas, but have not provided a comparative revolution to society to dignify the generation on. These later generations have only managed to continue or arguably degrade the status quo.