NU'EST was sadly one of those cases for a while. Some of their lack of popularity can be accredited to their label's poor promotions of the group and excessive activities outside of Korea, but NU'EST has actually continuously released music in Korea despite lacking promotions. There are sad stories of less than 100 fans registering for a lottery for their fansign, and they barely sold a thousand copies in first-week sales.
'Produce 101' season 2 changed that completely, and now they've become a rise-from-the-ashes icon. They've made history and accomplished things no one else has been able to. In fact, as Wanna One is only a project group, it could even be argued that NU'EST was the real winner from 'Produce 101' season 2 in the long run. (Of course, this would only hold if NU'EST can hold out their popularity.)
In fact, the NU'EST syndrome is so amazing that it probably wouldn't be exaggerating to say KBS planned 'The Unit' after seeing how big of a support and interest NU'EST got on 'Produce 101' season 2. The timing matched up too perfectly for it to be just mere coincidence.
But will 'The Unit' give birth to another NU'EST? The sad answer is that it probably won't.
Remember the almost-30 boys that were on 'Produce 101' that had debuted already? Yes, it's true that most of them had barely debuted, but then what about HOTSHOT or Topp Dogg? HOTSHOT debuted in 2014 and Topp Dogg debuted in 2013, not that much after NU'EST's 2012. Their fan bases weren't that much different.
For some reason, 'Produce 101' only highlighted NU'EST's story. Maybe it was because they've been out the longest. Maybe it's because all the members minus one were on the show to try again. Whatever it was, it was just a lot of many factors that happened to line up for NU'EST.
The first reason was that while NU'EST wasn't the only debuted ones, the editing made it look like they were the only 4 out of the 101 that had a sad debut story. It made people pay attention.
Second, NU'EST had at least one hit song in "Hello" and a rather decent discography. While other idols might have good discographies, no one had a hit like "Hello" did. And it helped even more that the hit was just a few months before hand, Rap Monster actually talked about "Hello", bringing it up to higher charts for people to listen to again. When people looked into NU'EST and heard "Hello", many people had already heard the song before.
Rap Monster singing "Hello" and saying it is his favorite song to sing in the shower:
Third, NU'EST managed to stick together and last throughout all their hard times. Nowadays, it's rare for an idol group that isn't in the spotlight to stick together so well, especially because their label can't support it. The NU'EST members are all the same age except Aron, who's from the U.S. and wasn't bound by the usual social age constructs of Koreans and basically treated the younger members as his equals. They're the rare idol that calls their dorm 'home' instead of 'dorm'. It's also a blessing that they were part of Pledis Entertainment, who wasn't a no-name company and could financially support NU'EST. A smaller label wouldn't have been able to do that.
Fourth, the NU'EST members are young. Aron debuted when he was 19 and the rest of NU'EST debuted when they were 17. Debuting so young means that even now, when they've gotten big, they're not much older than the groups in the spotlight now. As a comparison, they're actually younger in average age than BTS or MONSTA X, and around the same age as GOT7.
Fifth, all the NU'EST members had unique characters that attracted fans. JR, Baekho, Minhyun, and Ren all had their own stories during 'Produce 101' (even Ren, who had incredibly little screen time), and fans quickly found Aron had his own unique charms (aka "Oppa and me").
A lot of other things just sort of lined up perfectly for them, but lastly and probably the most important, they were the first to have this happen. It's the sad truth that once something has happened already, people just aren't as interested when it happens again.
'The Unit' participants won't even have the advantage of being a debuted group out of a bunch of trainees because everyone in 'The Unit' will be someone who has debuted already. And not just 100 of them – 500 of them. Some of them are in fact idols who have a decent fan base – Boyfriend, DIA, Dal Shabet, to name a few. The one group in 'The Unit' that could potentially be similar is Boyfriend. They've actually got most of the conditions that NU'EST had (although of course, editing will play a big factor).
'The Unit' probably won't make another NU'EST syndrome. KBS has actually had one of these projects before – 'My Last Audition' – and it didn't do so hot. For the sake of everyone who deserves the spotlight, I sincerely hope that I'd be wrong, KBS steps its game up, and it makes another superstar. Right now, it seems that the best that could happen to these 500 idols is that they at least have a chance for some screen time on TV.