Lmao... It's just because of the map. After around 19-21 seconds, if the activator is still sitting at spawn, they will be insta-killed, along with any REDS that are at spawn (hence why there is an explosion sound). This was the reason the first one lost.
For the last three, they all left. There is no disconnect message when someone leaves. I am not sure how you even got confused because in the video, you saw there was nobody on BLU, which means they left...