why it's a draw it's not stalemate


Your opponent ran out of time and can't win. You only have a king and the best result you could ever get is a draw.
If one player runs out of time and the other has insufficient material to mate, it's a draw.
In addition, a draw by stalemate only occurs when the person to move is not in check, and does not have a legal move to make. In the following link scroll down until you see stalemate and watch, https://www.chess.com/learn-how-to-play-chess#special-rules-chess