Waitlist isn’t automatic?

We’ve been members for 15+ years but have never used the waitlist tool until now. I had two waitlists for different resorts for an upcoming trip in September. I continued to check availability on my own as there were several resorts I preferred to the one I had reserved. While doing so, I found one of my waitlists came up as fully available! I was able to book it but was a little confused that my waitlist request hadn’t grabbed it automatically. Is there something I’m missing?