Anyone who's taken their children to McDonald's in recent years knows that "Would you like fries with that?" has been replaced by a starker choice: "Boy or girl?" Like the hot and cool sides of a McDLT, McDonalds knows that genders must be kept strictly segregated at all times for fear of a cooties outbreak that, if left unchecked, could have World War Z-level ramifications.
Thus, in the interest of public health—always McDonald's utmost concern— Happy Meal toys have been strictly gender-specific for the last several years. Boys get a football, a tank, or a tank that shoots footballs. Girls get a Barbie, a sewing kit, or a surplus boys' toy, spray-painted pink. These gender norms are strictly enforced, as everyone knows that if just one of those sewing kits falls into male hands, America's gender constructs will utterly collapse, and the next thing you know, women will be wearing trousers and men will start spending time with their children, and soon Western Civilization will be consigned to the history books.
So, for everyone's safety, when McDonald's added Adventure Time to its long list of tie-in Happy Meal toys, it put the show firmly in the "boy" category, excising all cootie-infested girl characters and limiting the toy lineup to Finn, Jake, Beemo, Ice King, and Finn and Jake again. Indeed, there's no Princess Bubblegum or Marceline to be found. (We assume nobody had the heart to tell McDonald's about Fiona.) In addition, McDonald's has alerted the authorities that Adventure Time's producers are in violation of Smurfette's Law, which requires all children's cartoons to either maintain a 99:1 male/female ratio, or consist entirely of female ponies. The ponies are not required to be pink, but it is encouraged.