>>6078637>Or more people join on an Apex stream and stay when they see someone is in the middle of a fight/at lower healthYou have a point there, it could really be an "emergent property" of a significant number of people joining in at any point at all and being "filtered in" by what you said "firefights / lower health".
As you and I cannot prove that without an experiment it is only an intellectual exercise to try to speculate about the real cause.
There is one experiment that could prove that beyond any doubt: enough anons (let's say, 500) arrange to meet in a stream and tab in, tab off in pre arranged times, and also do close the window and rejoin at other arranged time.
But that would likely trip the "anti bot" AI from Youtube and I wouldn't doubt if the stream or the whole channel doesn't get shadowbanned as a result. Youtube is a harsh mistress and a fickle one too, not one that people can experiment with impunity
There is another hint that "tab in tab out" can result in a viewer decrease: in any multi view collab this "wave" pattern happens when something interesting happens in some other POV and I doubt most are closing the stream outright, I assume people just keep the original one they intended to watch on another tab / window and tab off to the one with the action.