It's funny... Within the three types of early readers, the later category ("pretty close to finished product" readers) stay quiet until you're at the finish line...
I just dropped the link to the full PDF manuscript out to my prelaunch list yesterday afternoon, and wouldn't you know... many of the folks that have been quiet, never downloaded the intro PDF, didn't write an early review, etc... THEY are the ones who are now downloading the full book and - before I even follow up - have been publishing their early reviews!
The reviews keep coming in! All I had to do was say "I'm done with the book" and folks sat up and started to engage! 🎉