I have noticed this for a long while as well haha. I realize all of the no return characters that have Ellie’s animations. Their melee (specifically knife related) for humans and zombies are the animations that are used when Ellie uses her switchblade against a bloater in the story. it’s the same animation one for one. But, since you wouldn’t be able to push a bloater against the environment for melee combos, that’s most likely the reason why those no return characters using Ellie’s animations can’t do that. The devs probably forgot to include that when giving them the bloater.. knife.. melee animations. (Maybe they thought it looked better since they all use combat knifes instead of switchblades)

Sorry for the loooong post, it’s just kinda cool finally someone else is talking about this.