I mean Wikipedia offers basic information about some topic it's not like you are about to get deep insight unless you buy a book. And I bet Wikipedia generated millions of book sales like I said people who read an article from Wikipedia and went to Amazon or Google to search for a book.

If Wikipedia starts to receive commission for selling books the incentive changes from recommending the best book to the one who pays then the most

It's not about "who pays the most" it's about the best book. Book authors compete against each other to write the best book and therefore generate more sales.

Imagine reading an article from Wikipedia and at the end of the article it says "If you want to learn more about this topic take a look at our recommended books" and link leads you to dedicated page which lists let's say top 20 most popular books about that topic.

It can even replace Goodreads in a sense that Wikipedia community can rate, review and recommend books to each other.

Perverse incentives for book authors too. You could create a industry generating books to cite on Wikipedia.