Historians have the tendency to describe decades on an objective basis. It's possible to tell the story of the 17th century. On the first look it make sense to divide time into pieces of similar durations, 100 years are always 100 years. The problem is, that in the recent history the development of mankind has accelerated, which means, that in the same 10 years much more events are taking place than before. A well known example are the 1980s which are known as a very influential decade.
To understand why we have to snapshot first the situation before the advent of the 1980s in terms of media history. Until the 1970s the most common tools for producing information was a mechanical typewrite. This machine was used in private households, companies, by journalists and by scientists. Compared to a manual driven pen, a typewriter provides a higher typing speed and allows to create up to 3 copies of the original work. In general the speed of information distribution was slow, and the number of produced new letters, journals and books was low.
With the advent of the first home computers the situation changed drastically. The killer application for the first IBM PC was not it's ability to emulate a turing machine, but the first home computers were used as a modern typewriters. The early word processing tools were running only in textmode but they were powerful enough that in under 10 years the computer has replaced typewriters. Even people who were familiar with mechanical typewriters recognized very fast the advantages of the computers. It allows them to create information more efficient. Sometimes the early 1980s are described from a literature perspective as the beginning of the Cyberspace novels. What happened in that time, that the authors thrown away their typewriters, used a computer and wrote a new kind of stories. It's not possible to write a story like Neuromancer (1984) on a mechanical machine.
The replacement of typewriters was not the only benefit of the computer revolution. At the end of the 1980s a second revolution was visible at the horizon which was the Mailbox and Internet community. This kind of innovation was more drastically than using a computer as a typewriter. It was equal to replace the former postal service. All of these development took place in a single decades. In the 1980s there was more technical revolution available than the 3000 years before. That means, if somebody likes to describes in the correct depth, he has to write about the 1980s the same amount of books like about all the centuries before.
The assumption is, that this kind of revolution game has repeated in the 1990s. That means, in the recent history the amount of innovation has become bigger and a single decade contains of more facts than in the past.