I might have thought that but then Amazon kept the phone on sale after stock ran out, allowing to people backorder the phone. My guess is this is to eliminate most of the inventory but not a true "fire" sale. I suspect, with the phone being a year old, they are wanting to cut down on stock levels. With the phone being a year old, there will be even less interest in people wanting to buy the phone (other than at fire sale prices).
The good news, Essential has shown no sign that they'll stop supporting the phone. We are still getting very timely monthly updates, and the Android P beta seems to be pretty solid.