Wolverine Publicity

Everything About Fiction You Never Wanted to Know.
Although too small to see here, there's a line under the Mature Content label that reads "Wolverine does not appear in this issue."
"I stopped reading X-Men about the same time they started putting Wolverine on the cover of comics in which he didn't actually, technically, appear."
Lore Sjoberg, The Book of Ratings, "Marvel Supervillains (Part I)"

Certain popular characters within a fictional universe get used in gratuitous and/or inappropriate ways to enhance marketing.

Superhero teams in comic books constantly change. Characters join and leave so often that any given superhero team is often unrecognizable within a year. Other superhero teams have a Heroes Unlimited setup, where there are Loads and Loads of Characters and no two issues will have the same group. As a result, there are a lot more fans of particular comic-book characters than there are fans of particular comic-book teams or comic-book titles. Fans will like a new team book not if it has a name they recognize, but if it has characters they recognize. A new title will often sell based on whether it has already-popular characters in it, and existing characters will often be made more or less powerful based on how popular they are with readers.

This leads to one of the most overused tricks in comic-book marketing. When a character is very popular, they will often get Wolverine Publicity: appearing in every comic book title and format possible until the fans get sick of them. The character will often have a flood of mini-series which desperately search for something new to do with them ("in this issue, Wolverine visits Turkmenistan!").

The next step of Wolverine Publicity is random cameos to drive other titles. The promoted character will appear in the first issue of every new title, and appear in old titles with flagging sales, regardless of whether the promoted character makes any sense there. Particularly shameless marketers will just slap the promoted character on the cover and have them appear for one panel in the issue. They will often suffer from The Worf Effect; a new character hasn't "made it" unless they can thrash the most important character in the universe. Even if the story is actually a team-up, this pairing might suffer from being a Story-Breaker Team-Up since the promoted character may not fit in with the title's story or tone at all.

If a team has multiple titles, with different members in each one, the promoted character will somehow manage to appear in both titles—even if the two stories are supposed to be happening at the same time.

Compare Spotlight-Stealing Title, Billing Displacement, Overused Copycat Character, Red Skies Crossover, Lady Not-Appearing-In-This-Game. When an iconic villain shows up in an installment supposedly featuring someone else as the Big Bad, this becomes Hijacked by Ganon.

Not to be confused with the idea that Wolverine is becoming the focus of the Marvel Universe (although that certainly has spawned many examples of this trope).

Examples of Wolverine Publicity are listed on these subpages: