Everything dies out. Inevitably. Fallout got pretty popular, but with brighter fire means a faster burn. Unless you go to join a deeply dedicated and most usually small group, you won't find a huge cult following out and about, at least not normally. A franchise can be big and its fans can be casual, things we like dont have to be our whole world, that'd be a pretty bland and expectatable world after awhile. People play Fallout, its far from dead, but there isnt like a million member comunity or anything.

True

It's been 7 years since the last Fallout game, so it's normal that interest has decreased. I think the show has attracted a lot of new fans, a lot of them have also visited the wiki for information, but haven't taken part in discussions.

Yeah. Someday it might pick back up again.

Interest in everything waxes and wanes. That's normal. While new additions encourage attention, periods of dormancy are not unusual. Also, consider that it's summer, and many people have other interests (gasp!) such as outdoor sports, chores, vacations, or family obligations.