So when there was only 15 secs left, I got 4xxx points and my opponents only got xxx points. Then I was told I was lost (because I got no possible move I assume

So when there was only 15 secs left, I got 4xxx points and my opponents only got xxx points. Then I was told I was lost (because I got no possible move I assume) and he was won, but that is really a bad game-winning condition because there was no way my opponent would got 4000 points in 15 secs. So why not let the game clock finish before the game tells who is the winner?