I'm not sure how much more time to give to this, since people have tried to explain this to you multiple times, and you've been rudely dismissive throughout. It appears that some of this is due to ignorance, but your attitude is all you.
But on the off chance this is worth it: Games provide mechanical incentives to encourage the sort of play the designers want to see in the game.
- Old school D&D, for instance, gave XP for accumulating treasure not for killing monsters, which incentivized sneaking around, stealing stuff and running before the monster found you.
- Later versions of D&D instead gave D&D for "overcoming obstacles," which incentivized overcoming foes by whatever means possible and, as a result, made treasure a lot less appealing unless there was something to spend it on (see the relevant mega-thread for more on that).
- In 5E, inspiration is supposed to be given out for clever play or roleplaying, which helps incentivize those. (In practice, advantage is so easy to get in 5E, lots of DMs don't bother with inspiration.)
- In other, non-D&D games, characters sometimes get XP or plot tokens (inspiration counterparts, but often more powerful) for failing a task, incentivizing trying all sorts of stuff, with the expectation that bravery and recklessness is the path to future success.
To emulate something like the Adventure Time TV show, there should be mechanical incentives -- the equivalent of inspiration or XP or something else entirely -- for confronting feelings, dealing with hard truths, bonding with friends, making exciting discoveries. None of those are really covered by anything any version of D&D has done, so either new incentives would have to be created, what rewards XP would have to be changed, or both.
As listed, and as stated earlier, the incentives in 2E D&D, which Pendleton Ward says is what inspired Adventure Time, are to kill stuff and take their treasure. Whether or not D&D was what inspired the show, those incentives would lead to PC behavior that doesn't match the Adventure Time fiction. (It would certainly change the relationship between Finn, Jake and the Ice King, for instance.) While players can and do sometimes ignore incentives, counting on them to ignore the rules of the game for the sake of the fiction is asking the many mechanically minded players out there to play the game "wrong." Better, instead, to create mechanical incentives to play the game "right" and match the fiction.
