I will preface by saying this is not a perfect theory, and that for the most part it only refers to gen 4.
Now the overall idea is that boy groups starting from gen 4(though you could argue for late gen 3) have become increasingly insular in their content. This is not saying that their music or variety has become worse or more self indulgent, but rather that Companies have increasingly geared boy group content to cater to the fanbase than to the public.
Now one would argue that all group content is primarily geared towards the fandom first, and in certain respects you would be correct... HOWEVER the means of distribution is substantially different.
It's no question that BTS is more or less the blueprint of social media engagement for boy groups. However, BTS' media engagement wasn't entirely just social media and company produced content. If you're an old enough army, you would remember the time when RM was the most known member of BTS due to his constant time on variety shows.
And that is where I feel that a lot of 4th gen boy groups have been lacking. Their permeation in general Media is almost zero.
A different example is how quickly DKZ member Jaechan absolutely propelled the group's overall interest through the roof following Semantic Error.
Nowadays there's tons of Boy Group Reality Shows, Vlogs, and Variety specials... but almost none of it in general tv. Going back to gen 3 and especially gen 2, you could find countless male idols all over regular broadcast and film. You may be wondering, if that's the case, why hasn't it affected international fandoms? And the answer is fairly simple... we international fans have always interacted with kpop groups in this format. There's no fundamental change on our side of things cause it's always been via online video and social media that we've gotten this content.
And I feel that ultimately is what has caused an erosion of Public interest in Kpop Boy Groups. It's not cause the music is too noisey or that boy groups are all the same, or that men care even less about other guys now. I posit that companies have essentially created a media bubble around their boy groups which has had the adverse affect of making them a mystery to the general populace who aren't going to go onto youtube dot com to look up boy group #765