I don't know if this has ever been really discussed or discovered, not so much the increase in album sales but the cause(s) behind it.
But it is a peculiar one: up to a certain moment you'll see a gradual increase in album sales. And then suddenly, a huge spike happens, or maybe better said a paradigm shift.
And it's not just for a few groups, but across the board.
When you check the Circle chart over the years, it becomes evident:
Annual Circle chart: 1st rank - 5th - 10th - 20th - 50th
2016: 750k - 350k - 225k - 105k - 60k
2017: 1.5M - 610k - 330k - 160k - 70k
2018: 2.2M - 640k - 350k - 240k - 90k
2019: 3.7M - 550k - 410k - 270k - 110k
2020: 4.4M - 1.2M - 670k - 470k - 170k
2021: 3M - 1.6M - 1.05M - 710k - 270k
2022: 3.4M - 2.1M - 1.7M - 1M - 270k
If it's just 1-2 top groups experiencing a popularity boost, an album release that's hugely popular, or a lot of the top groups releasing an album in the same year, this will logically influence the Top 10 of that year.
But what you see in 2020 (and 2021) is a sudden, huge rise in album sales across the board.
Has the cause of this ever been determined?
Was it a global Hallyu Wave spike (but why then 2020, and why then the lesser known groups profiting too)?
Was it China and Chinese fanbases that embraced K-pop?
Was it album pricing or a change/increase in distribution outlets, making them more accessible for non-Koreans?
Or something else?
I'd love to know if the revenues from album sales increased to the same exact extent over the years or if there's a difference with the amount of sold albums - but unfortunately those aren't as easily accessible as the Circle chart.