why do some games end in a draw and some end on a win after the OPP. time limit?


You are probably talking about timeout vs insufficient material
in a game where your opponent times out, you will only win if you have enough material to checkmate the opponent—even if it means they make significant blunders
however if you dont have enough materail to checkmate the opponent, then it is considered a draw since there is not sufficient checkmating materrial.