I'll give it a shot. They're going to keep doing it because they keep getting away with it. You've tied this to (I'm assuming) your real identity, so that makes it a little more difficult to call them out because they can respond. But if you don't let us know, we can't know to avoid them. Even avoiding spending time getting to a final round, only to be asked to do this, would be helpful.
They got you to work for free. They probably didn't benefit directly unless you gave them new ideas they didn't know about before, but you still put the time in. It was work to you. And they obviously didn't respect it at all, much less take the time to read your resume. Maybe they weren't even interested in hiring you?
The only saving grace for that could be an exceptional position with great responsibility and great pay. But even if that's true, they flippantly sent you through interviews for that position, so they're likely a bad company from the inside. They only way they would face consequences is if they're named.