Isn’t that a continuation of “why the outlier was culled”?

Not sure I follow, but I think the answer is “no”.

If you control for all the causes of a difference, the difference will disappear. Which is fine if you’re looking for causal factors which are not already known to be causal factors, but no good at all if you’re trying to establish whether or not a difference exists.

It’s really quite difficult to ask a coherent question with real-world data from the messy, complicated reality of human beings.

A simple example:

Women are more likely to die from complications after a coronary artery bypass.

But if you include body surface area (a measure of body size) in your model, the difference between men and women disappears.

And if you go the whole hog and measure vein size, the importance of body size disappears too.

And, while we can never do an RCT to prove it, it makes perfect sense that smaller veins would increase the risk for a surgery which involves operating on blood vessels.

None of that means women do not, in fact, have a higher risk of dying after coronary artery bypass surgery. Collect all the data which has ever existed and women will still be more likely to die from the surgery. We have explained the phenomenon and found what is very likely to be the direct cause of higher mortality. Being a woman just makes you more likely to have that risk factor.

It is rare that the answer is as neat and simple as this. It is very easy to ask a different question from the one you thought you were asking (or pretend to be answering one question when you answered another).

You can’t just throw masses of data into a pot and expect sensible answers to come out. This is the key difference between statisticians and data scientists. And, not to throw shade on data scientists, they often end up explaining to the world that oestrogen makes people more likely to die from complications of coronary artery bypass surgery.