In my English book, there's a text that talks about how rainforest plants being used as remedies. More specifically, it talks about how they become more and more common in modern medicine, while the indigenous tribes have been using them for a long time. In the conclusion of the text, it says:
Rainforest plants were being used by native Indians long before the Europeans arrived. Unfortunately, it has taken us nearly 500 years to realise the value of these ancient medicines!
What I don't understand is why the past progressive is being used here. As far as I know, the past progressive is usually used to describe an ongoing action at a particular point in time in the past, or two longer actions that were happening simultaneously. Neither is the case here.
I personally would have used the past perfect to indicate anteriority to the arrival of the Europeans.
Any thoughts why the author may have chosen the past progressive?