Along with the announcement The Walking Dead is ending with season 11, AMC also announced a spinoff series for Carol and Daryl - a decision that only highlights the big problem with the show's other characters. Though the main series is ending, AMC is by no means finished with The Walking Dead as a franchise. In addition to Carol and Daryl's spinoff, there are plans for an anthology series, Tales of the Walking Dead, which joins AMC's other spinoffs, Fear the Walking Dead and The Walking Dead: World Beyond. Not to mention, there are still those Walking Dead movies to come featuring Rick Grimes.
The Walking Dead has been on the air for a decade now, and in that time, many characters have come and gone. Carol and Daryl, of course, are the exceptions, having stuck around since season 1. Since then, only a handful of characters have received the same level of development as Carol and Daryl, and most of them are either dead or will be appearing in other Walking Dead projects. The rest, well, they're the very problem - most of The Walking Dead's recently added characters are not very memorable and are not going to drive interest in a spinoff show.
It's no secret that characters die on The Walking Dead, and as such, cast turnover is inevitable. In season 2, the show killed off two main characters, Dale and Shane, but had also gained a handful more in Maggie, Hershel, and Beth. That pattern is then repeated, more or less, across its 10 seasons: characters leave (mostly likely killed), and new ones arrive to take their place in the ensemble. For the most part it's been a successful strategy, but whereas some additions like Michonne and Abraham proved popular, characters like Tara, Gabriel, or Aaron never gained the same following among fans. Which isn't to say they or any other character are inherently bad or the performances their actors give poor, it's more that The Walking Dead hasn't invested in them and so viewers are given little reason to care.
Take The Walking Dead season 10, its most recent, as an example. With the survivors embroiled in the Whisperer War - by far the show's most compelling plot in years - the best material was given to main characters Michonne, Daryl, Carol, and Negan. Meanwhile, Rosita, Gabriel, Aaron, and Eugene were largely sidelined, with storylines that were more plot-driven than character. Storylines like Dante being a Whisperer spy, Eugene making contact via the radio, and Aaron briefly befriending the Whisperer, Gamma, worked to drive the narrative but did little to further them as individual characters. Even Ezekiel was handed a storyline, his thyroid cancer diagnosis, that has just one, inevitable outcome and isn't likely to spur any calls for him to lead a spinoff.
By comparison, season 10 sent Michonne on a journey to possibly reunite with Rick; had Carol grapple with wanting revenge for Henry's death; Daryl mentor both Judith and Lydia and take a romantic interest in Connie; while Negan continued to make amends and prove himself trustworthy by infiltrating the Whisperers and killing Alpha. For these characters, season 10 challenged them, forced them to reckon with past decisions, and reevaluate what it is they actually want. Now, the interest in seeing where Negan's story goes next lies not just in what happens, but in how he adjusts to being a more accepted member of the group. Whereas the interest in Eugene's storyline, for example, isn't so much his meeting with Stephanie, but the discovery of a new community, the Commonwealth. The former is driven by character, the latter by plot.
Carol and Daryl are the obvious choices to lead a spinoff because even without knowing what the show is about, their characters are enough to create interest. Even with how much The Walking Dead has already done with Carol and Daryl, they are characters who audiences will watch regardless of the situation. And yes, the development they've received is in part due to their longevity on the show, but Aaron, Eugene, Gabriel, and Rosita were all introduced prior to Negan and none are as popular. In fact, characters like Negan and Maggie are the exception here - popular characters who AMC haven't given spinoffs, or even hinted their stores will continue elsewhere. Yet, while there's a discussion surrounding what their futures will be, the same cannot be said of most other Walking Dead characters. Perhaps someone like Rosita or Eugene will appear in an anthology episode, or Connie joins Daryl in the spinoff, but they aren't characters who can carry a series alone. None of the newer characters on The Walking Dead are enough to keep either the main show going or lead another, and by greenlighting a Carol and Daryl spinoff, AMC clearly agrees.