Why are abbreviations like BRB, TBH, and IDK appropriate in some situations but not in others?

Dont talk in abbreviations to elders, most of them might not know what that means and youll likely have to teach them

the major difference between the two is the objective and the reward of the game. candy crush has a puzzle theme with the objective of meeting a specific quota of points or objects, you are able to gain access to the next level and compete with peers on the process. on duolingo the objective is rather different, you are given sets of questions for you to answer for you to move to the next level and as for the reward, you are able to learn available language as this is an app developed to teach the user about other languages.