Why is the question "Is there free will?", and not, “What is free will?"

I'm a layperson interested in the problem of free will. I recently started reading one of the popular introductory textbooks to the subject. I'm halfway through, and while the book did describe a few of the most notable approaches to the problem of free will, there is something that surprised and disappointed me, which I'll describe below. Because I'm a newbie, I'm wondering whether this is happening because I'm missing some basic understanding, and if so, I would like you to explain it to me. Almost all of the discourse in that book, as in most popular discourse on the subject, focuses on the question "is there free will?", attempting to argue that the answer is either yes or no with various arguments. I was surprised and disappointed that little attention is devoted to the question "what is free will?" It seems to me that "free will" is a concept that we all strongly feel, but it's difficult to provide a definition for it. People might say that a choice made under free will is one where the person making the choice did what they really wanted, and wasn't coerced by anyone to make a different decision. The problem is that this definition uses the terms "wanted" and "coerced" which are equally as mysterious as "free will". I was therefore disappointed when most of the approaches presented in the book did not focus at all on defining free will. Why should I trust any philosopher's argument for the existence or lack thereof of a concept that the same philosopher hasn't been able to provide a definition of free will? I can accept that the problem of defining free will is very hard and we don't have an answer yet. I just don't understand why the main discourse isn't to discuss the problems that prevent us from defining free will.