The drive to turn children's TV shows into something adult-themed

Many adults nowadays like watching children’s TV shows. Sometimes this is due to the nostalgia factor associated with a beloved show from childhood, whereas other times, adults will start watching a show in adult age (as happened with both "My Little Pony: Friendship is Magic" and "Bluey," for example). Either way, it’s common for adults watching the show to attempt to put a more adult-themed spin on the plot or characters than was initially intended, by adding more violent, sexual, or all-around disturbing content. On the simplest level, this can take the form of disturbing fan theories or memes about children’s TV (such as the "Rugrats" theory that everyone is dead except for Angelica); but it can also be more extensive. For instance, the "My Little Pony" fanfic known as "Cupcakes" was a well-written story whose entire purpose was to make "My Little Pony" violent. This story was so successful it spawned an entire subgenre of "grimdark" fanfics, in which each of the main characters from "My Little Pony" took turns playing the role of a bloodthirsty villain.

The question is, why are adults so interested in making adult-themed versions of popular children’s shows, especially when there are so many gritty, adult-oriented TV shows out there? If the adults are watching the children’s shows because they like wholesome entertainment, then why post adult-themed fanfic or memes about them at all? Is there something about the union of children’s shows with dark themes that is exceptionally appealing, and, if so, are there certain characteristics that make particular shows most likely to be used in this way?