Good question y not.
“What about those who change their gati without ever having heard of Buddhadhamma?”
Yes. We all have heard such instances where Buddha Dhamma is not involved. Especially, some criminals “come to their senses” in some cases and drastically change their behavior.
– Some people give up bad gati like smoking, drinking, or other bad lifestyles.
However, the point is that the root ignorance about the “true nature the world” cannot be removed without comprehending the “unfruitfulness” and “dangers” in the attachment to worldly things.
– A criminal changes for the better by seeing that his life could become even more miserable by continuing with the same actions/behavior.
– Same with those people who give smoking, drugs, etc.
– They would be just “looking for a better life.”
Comprehension of the anicca nature is different. Of course, giving up all those bad habits mentioned above is the first step.
– This is not an easy point to get across.
I recommend re-reading the first part of the following document where a large amount of hidden anusaya is removed by a Sotapanna: Waharaka Thero Discourse – The Way to Nibbana