When people have unexpected success, critics like to rationalize it away. I have seen it with the Backstreet Boys. I already discussed age. ( see link below), But I wanted now to discuss another bias, their apparent lack of solo success. I say apparently because even though Nick Carter was not the breakout like Justin Timberlake, he has amassed a solo following AJ. In fact, AJ was the first to perform by himself as his alter-ego Johnny No Name in the 90s, although he never released anything then. Brian's Christian album ranked high on those charts and probably brought in those who never would listen to that type of music. As Hanson proved, you don't have a large mainstream following doesn't mean you are not successful. The problem is if you're not mass-market, the mass market won't acknowledge your success or even existence.
The Backstreet Boys are unique because they are one of the few groups that have continuously managed to stay together a long time. Others h broke up and reunited much later. People who criticize them for remaining a group don't realize how hard it is to sustain a healthy group dynamic for a long time. Some group members feel like second fiddle. Therefore, they leave out of resentment. Some only use a group as a stepping stone to a solo career. For example, Nicole Sherixnger made clear in her Facebook page bio that was all the Pussy Cat Dolls were to her. That's probably why she was the only singer in that group with a bunch of backup dancers. There is also the danger of being swallowed up by the Borg-like hivemind. Harry Styles felt he sacrificed too much of his identity in One Direction.
On the other hand, the Backstreet Boys have so invested in each other that permanent separation was an option to deal with these potential pitfalls. They admitted they needed time apart to feel united again. That is true with any healthy relationship. Solo projects are another key to maintaining individuality but were never the initial aim. In fact, if Nick didn't venture out first, I doubt the others would have apart from AJ because AJ has the perfect solo personality and previous experience. I always suspected that Kevin never released his solo album because he liked the comfort of a group, whether he was singing or acting while away from the group. Being a perfectionist makes you feel more exposed without the cover of others. Nick found out how hard the transition from group to solo can be tricky with unrealistic expectations. Even Brian he felt strange doing his first solo video. He probably wants his son Baylee to start out solo to avoid that awkward transition in addition to easier decision-making.
Howie also mentioned sacrificing ego. He should know after being involuntarily demoted from the lead. I am sure that hurt at first, but Howie made peace with it to his credit because he was always essential. . His harmonies are crucial, as one person noted. He also got more leads during Kevin's absence and even sang Kevin's parts.
The Backstreet Boys cohesion that allows them to go between the group and individual projects should be celebrated. In addition, it shows what is possible for others if they adopt the proper perspective.