Under My Home -> Account -> Online Chess Settings, there is a setting called Auto-win on time. If the box is checked you will automatically win on time. If it isn't checked, then you have to manually claim your win on time.
Claim win on time button

In 2024, the setting is now at Settings > Daily Chess > Automatically claim victory when time runs out
https://www.chess.com/settings/daily
I have lost a few games because I was late few minutes in responding
and sometimes I win on time because my opponent did make his/her move, but what if my opponent or I want to continue the game.
My point is why does the game end automaticlly on time, I think there should be a claim win on time button so that even if the time is finished you can continue the game.
For example if your time is finished and your opponent is not online you can have another chance to move.