Think about it this way. I'll give you examples.

Scenario 1

Climber falls while leading and his last draw breaks (equipment failure). Get's injured. MAIN cause FALL, SECONDARY EQUIP FAILURE
Scenario 1 doesn't occur if the person doesn't fall.

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Scenario 2

Climber takes a take and loads his draw. It breaks (equipment failure).

Main cause is equipment failure.

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See the difference?

Not necessarily. You can be 'taking' on a piece or using it as an anchor.

Have to think about it in terms of Main cause and secondary.

Exactly. Not many people are going to be taking out ropes that are on the verge of breaking without something happening before. When they do it's going to happen when taking a fall.

You have to think of equipment failure as a MAIN cause.

For example a typical failure may be on a quick draw. That draw is only going to break once there is a big load on it. So would happen during a fall. It would then be categorized as a secondary cause.

How have you always known? Do you have an actual source of data which says the opposite?