Long post, but the thing is that in this thread everyone is right and wrong at the same time, so guess i'll try to explain a bit (?).
While the music was inspired in the west, the visual aesthetic was mostly inspired in Japan, which had its own very different trends at the time, heavily inspired in anime as well as the 80s as it was a golden era for their media and so it established most trends that would then be followed for decades and are still pretty die-hard. But regardless:
Although Korea's economy "boomed" in the 60's, the wide majority of its population was poor for a majority of its modern history as a product of japanese occupation-then the korean war-then the military dictatorships which except for Park Chung-Hee (the one behind the "boom") focused on just holding on to power and little else, leaving the country mostly undevelopped. So it wasn't until the late 80's and 90's, with the slow transition into democracy and liberalization of the economy that it started reaching other demographic groups aside from the wealthy and the government.
This involving also liberalization of the media which had been heavily monitored for decades by conservative/pro-government businessmen who monopolized a majority of media becoming a circlejerk of very similar content over and over and over again. Only really growing in the 90's when, with the fall of the dictatorships, these businessmen slowly lost more and more power, creating a vacuum, filled by their rivals as well as by new actors and characters of many backgrounds as well as lesser businessmen that finally had the opportunity to grow, allowing other ideas to flow into the market for the first time in a long while.
All of which brought what koreans define as their golden era in most forms of media, whether it is dramas, tv shows, films, or music, you will see that a majority of the media-related records in korea were all achieved in the 90's and never reached again - except for some which were only recently broken.
So yeah, Korea was technologically advanced, and rich, statistically speaking, but that wealth didn't reach most people much less so did the technology, until the late 80's and early 90's. Most of it had been focused exclusively on industrialization and the conglomerates as well as those close to the government and their business of interest (cars, manufacture, electrodomestics, we all know which ones i'm talking about) but nothing else aside from what had already been established as a moneymaker. But at the same time, the early 2000's korean content wasn't really backwards, it was just different, and based on a mix of what had succeeded domestically in:
-Korea's 90's golden era (which was an experimental clusterfrick of things from all the way back to the 20's big band to 90's techno)
-then the US (both from the 80s - which was a golden era of media for the US and was the era most of those artists or their producers grew up during and drew inspiration from - and whatever were the current trends at the time)
-and Japan, who was - until the 90's crash -, far ahead of the west too in many areas but was just different. And the talk about Japanese media is a whole other topic that would take too long.