like all young celebrities, they all tend to fall and eventually be forgotten because he's a tool for the media. The music industry these days will give record deals to anyone who has at least one song that could be considered by the masses as a "hit". As his hit single becomes popular, his hype increases as he makes public appearances, commercials, interviews, TV shows, endorsement deals, etc.
When the single starts to wear off and his place in the charts start to fall, these kind of celebrities try to grasp themselves from any kind of spotlight they can find in order to maintain their "relevance" because they realize they have no true talent to stay top by being just a singer, but from the propaganda they generate. Some celebrities even go to unbelievable depths in order to be front page news, they do drugs, DUI, get into car crashes on purpose.
Brian Johnson, you don't know him 'cause he doesn't do commercials, or gets interviewed all the time, or even considered "mainstream", but he's one of the most influential singers of all time and has the second best-selling album of all time 'cause he has the talent to attract billions of fans worldwide just by singing.