Maybe so, but passion doesn’t pay the bills. You can work on improving your writing and working on passion projects on the side. But you were talking about creating a writing career, which is different than doing it for passion, it is much more analytical and business-oriented.
Samples aren’t “free work” because you are welcome to publish them on your blog, pitch them to publications and use them for gaining clients. They serve a specific purpose, you did not write them for free for a “client” to prove yourself.
In any job, you need to be able to show or explain in some way that you can handle doing the job, which is the purpose writing samples serve. No one is going to pay you money to write for them if you have nothing that shows you can string together a coherent sentence.
Just like if you design clothing, you need to show pieces you’ve designed, or if you are an interior decorator, you need to show places you’ve decorated and styled. It’s not “free work” it’s basically proof of concept.