Back in the 1990s (insert OldManYellsAtCloud.jpg), TV dramas were episodic. There was an overarching plot that occurred in the season premiere and finale, but the bulk of the series would be one-off villain of the week episodes with a teaser at the end reminding you of the big plot. In X-Files, Fox Mulder would spend the entire episode investigating a lizard monster but at the end of the episode, he would find a document belonging to Cancer Man. But if you missed a random episode, no big deal.
In the 2000s, TV dramas became serial. It started with Sopranos, Lost and The Wire, where an entire season would tell a single story. If you missed an episode, you missed a key part of the story. As technology advanced and DVRs/streaming services became widespread, more shows were becoming serial. By 2012, every show wanted to be the next Breaking Bad.
Conversely, back in the 1990s movies were self contained stories. When you walked out of blockbusters like Forrest Gump or Braveheart, you weren't speculating what would happen in the sequel. It was a great story in and of itself. But as CGI increased the cost of special effects, movies would only be greenlit if they had a built in audience. This ushered in the the comic book era, Lord of The Rings, and Harry Potter series.
Then in 2012, a movie came along that changed the industry. The Avengers introduced the concept of a cinematic universe, with characters having individual movies while combining in a single film. This prompted the audience to watch not a single film, but 5 films to enjoy one.
In addition to Marvel Universe, there are now plans for DC Universe, Sony Spiderman Universe, Star Wars Universe, Monster Universe (2014 Godzilla), Dark Universe (Tom Cruise's Mummy).
Further, it's now become standard to include post credit scenes that advertise the next film. Each film in a cinematic universe features it's own stand alone bad guy, but in the post credit scene it advances the over-arching plot of the series.
The invention of the cinematic universe is actually a regression to the episodic TV shows of the 1990's. Is there any difference between a post credit scene with Thanos grabbing a glove and X-Files going to credits as Cancer Man watching Mulder on a hidden camera? No.
Cancer Man has become Thanos.