Haha! Good question. I don’t have great answers, just guesses.
1. One Direction came at an incredible time in the convergence of pop culture and technology. Social media was beginning to change our lives forever, yet there was innocence and naïveté about it all, and a freedom to express oneself— and therefore a naïveté to believe. The boys created an intimacy with fans that made them more accessible than any band before or since.
2. The band members had both personality and looks— there’s no lemon amongst the five of them. They were relative virgins in the industry. They weren’t polished or manufactured, and this freshness was apparent in every interview. They were five baby animals that couldn’t be herded or tamed. Since then, the desperation to recreate One Direction always resulted in the boys themselves not having the same chemistry, or in management over-managing.
3. Previous to One Direction, a band’s fandom outreach was slow and inefficient. There were no Tumblr, Twitter, Snapchat, WhatsApp. The turnover for rumors, gossip, contests, charting was slow. Bands rose more slowly, had more time for trial and error. As a result of technology, One Direction rose like fireworks. There was pressure to create content as fast as possible. There was pressure to manufacture constant news/ stunts/ gossip.
4. Since One Direction, fandom relationship to bands has been utterly transformed. Fans are no longer passive consumers. They have the internet at their fingertips. Facts can be verified. Manipulation is now a standard part of fandom. Cynicism is par for the course. Stunts are no longer so easily believed.
5. These boys have extraordinary charisma. In addition to being able to sing in harmony and acrobatically, they are also disciplined, kind, restrained, nice to fans. They behave. They keep bad news out of the spotlight. They are charitable. They are gentlemen. It distinguishes them from other teens who come apart under the spotlight, away from parental guidance.