Scenes placed after the credits were once a genuine event and are now a routine expectation. The device lost its effect through the same mechanism that made it popular.
It worked because almost nobody stayed
The original appeal depended on most of the audience leaving as the credits started. Those who stayed received something the others did not.
That asymmetry was the whole point. The scene was a reward for a small group and a rumour for everybody else.
Once staying became normal, the reward became a queue. Everyone sits through several minutes of credits to see something everyone else will also see.
The surprise cannot survive publication
Descriptions of these scenes appear within hours of any screening, and dedicated pages exist purely to report whether a film has one.
A device built on not knowing cannot operate when the information is trivially available before a viewer buys a ticket.
Studios responded by using the scenes for announcements rather than surprises, which is a different and much weaker function. An announcement works just as well when reported second-hand, so there is no reason to be in the room.
It became a structural obligation
Audiences now expect a stinger in whole categories of film, and its absence reads as an omission rather than a choice.
That expectation forces material to be created for the slot whether or not there is anything to put there. The result is scenes that gesture at future films without content.
A device that has to appear every time cannot be an event, because events are defined by not happening on schedule.
Connected storytelling changed what it carries
When these scenes introduce elements of a larger ongoing story, they function as advertising for a future release placed inside a completed film.
That works while the audience is invested in the wider story and fails as soon as they are not, at which point the scene is simply an obligation delivered to nobody.
It also weakens the ending it follows, since a film that has just resolved is immediately reopened for commercial reasons.
The credits themselves are the collateral damage
Holding an audience through the credits was once a side effect that crews appreciated, since their names were being seen.
In practice the audience now waits rather than reads, filling the time with phones and conversation. The presence of the crowd is not attention.
The device that appeared to rescue the credit roll has instead turned it into a waiting room, which is a worse outcome than the empty cinema it replaced. Names now scroll past a full house that is looking at something else.