Looking back, the steep decline of Kim Gun-mo's 5th album is quite strange

Every singer tends to have an album that marks a sudden downward trend.
For Byeon Jin-seop it was the 3rd, Shin Seung-hun the 6th, Kim Won-jun the 4th, and Yoo Seung-jun the 6th...
But among them, Kim Gun-mo's 5th album was particularly extreme.
True to his reputation as an album sales monster, it still sold over a million copies,
but that was due to the era's characteristics where million-sellers were pouring out
+ the reputation of Kim Gun-mo's previous albums.
However, his perceived popularity dropped quite dramatically...
While "Speed" from the 4th album isn't talked about much now,
it was an undeniable massive hit at the time.
But "The Bird That Flew Over the Cuckoo's Nest" from the 5th album
probably wouldn't even make the Top 30 hits of '98.
It was the first time I saw a singer at that level of peak popularity experience such a vertical drop.
I wonder if he should be viewed as a victim of the Idol era...