Wow, that's a massive tournament.
For better or worse, this is how those multiplayer tournaments work. Once it reaches the point where there is only game currently playing, the number of qualified players will be whatever is needed to fill out the final. So in this case, one qualified player plus the four ignored players make up the final.
Also note that the final obviously works differently too. Here the goal is simply to finish first to get first place.
Unfortunately the way it works is not communicated anywhere. People may assume that the tournament will just keep eliminating the same number of players (which would make for a lot more games towards the end).
The system for who gets ignored is not communicated either. From what I understand, the people who finish first in their games avoid being ignored in the next round. Then once a player has been ignored, they can't be ignored anymore unless there is no choice.
The system seems to be so that the players who win all their games will usually only be ignored in the game right before the final, which is usually the best time to be ignored, since like you see here, only one player could qualify in that game. It is as if the players who have to play that semi final game have to win two 5-player games in a row in order to win the tournament, making their odds much lower than those in the group of ignored players.
Unfortunately you got included in that game and didn't realize that you needed to win it to qualify for the final. Which is probably a very common issue for those kinds of tournaments.