I don't know much about this author. I'll give that author the benefit of the doubt and say that they are a great author, but very much unknown by readers.

Now my question is: why would the situation be any different for the author if the virtual library didn't exist? Just because a book is lent out, doesn't mean the book was read. Maybe the reader didn't have time. Maybe the reader finished the first chapter and found that it didn't suit their tastes. Yes, that can happen with purchased books. On the other hand, I'll suggest that it is much more common with borrowed books. People are much more likely to take something that is free, even if they don't really want it. People are far less likely to pay for something that they are uncertain of.

I would suggest that the author needs to look at how they can get their book to their customers, rather than complaining about libraries. Libraries may be a useful tool here, or they may be getting in the way. Libraries may be a way to get their book in front of their readers. If they like it, they may buy it. If they like it, they may discuss it with friends who will buy it. Your foot is in the door. Of course, the library may be full of anti-social leeches who would never spend a dime on a book. But there is not much that you can do about that.

Of course the thing that the author really has to work on is getting people to buy the book from the store front. Presumably people who are at the store are interested in buying, while library patrons may or may not be interested in buying. So the store customers are the important ones. In that case, the author has to ask what does it take to get noticed? When they are noticed, they have to asked what does it take for the customer to read their advertising literature (e.g. the blurb, positive reviews, etc.)? When they are reading the advertising literature, how does the author translate the customer's interest into a transaction?

You see, those six sales tell me something: it tells me that the author doesn't have a clue on how to sell their product in a competitve marketplace. (I'm not saying that I do either, but I do something else for a living.) Even a moderately successful salesperson would be able to sell more than six copies, even if the product is truly horrible. That author, who I already assumed was a good author, should be able to do as well or better once they acquire the skills to do so (or hire someone who does).