I am not an expert for avocados, but I suspect that they do the same as with most fruits (I worked in fruitpicking while backpacking):

apart from herbicides, fungicide and pesticides, there are chemicals to block the ripening while the fruit is still on the tree, because you want to harvest all fruits at once. And then you do various things for packaging.

And there were likely other purposes as well, I have forgotten now. All in all, lots of them were used, way more than I expected. So much, that I prefer organic.