That's because the score you see on your screen is not the globally accurate score, it's just a representation of what the score was at some point. Because of latency between players and the server, it's impossible to maintain everybody's score they're seeing on the screen as the actual score being kept by the game's server. So it's not as simple as just 'calling it when it reaches zero'. Think of it like voting. Voting ends a 6pm, and even though at 6pm Team A is in the lead, votes are still being counted from all sources. Once they're all counted, Team B wins the vote. Regardless of the count at 6pm, the final count is true. What is [i]not[/i] happening, (which you seem to think is) is votes being accepted at 6:01pm, after the 6pm deadline. This isn't people getting a kill at 1 second after the game ends, it's the game server failing to update satellite displays in time for the player to see it. You're not being robbed of a win, you were just unlucky.
I don't doubt that this happens, but don't go acting like it's every other game. It needs to be a pretty damn close game for it turn over that quick and close games are already a rarity on their own.