Does anyone know how the aggro system works?

As the title goes.

I've been wondering this question for a few years by now and never found any real answer.

Whenever I am in an event, I will more or less always be swarmed by enemies while everyone else is able to just wall by and not worry about being chased down.

Happened last night in Test your Metal event in which harvestbots loved flaming me and following me over everyone else. It was awful as my armor did break at that point, at least one piece did which isn't as bad.