Draw Games

Why is it that more often than not, If I run someones clock down to nothing, even though I am losing, It will be determined to be a draw?

It does not even matter if they have 3 queens (this has happened) or multiple pawns, a rook and a queen, etc. The opponent has more than enough in their arsenal to win the game, but lost on time!

They LOST on time!!!.........But it is a draw.

I would like someone to explain this. I have had games called draws when I was clearly winning, and constantly placing my opponent in check, move after move.

Always, Always, it is when my opponent has ran out of time.