Another factor is that people who buy the D2 (or the D1 before that) tend to sort of drop out of the DAC arms race. It's kind of like when someone gets in to Stax gear, or gets a super nice tube amp from Eddie Current or ECP Audio. They tend to stop worrying about the flavor of the month or whatever new releases might show up and become "hot" - they know the gear they already own is extremely good, and they have no desire to look elsewhere. That tends to make people participate less on the forums.
I feel that way about my D1. I have been tempted to get the D2 a few times when they have showed up in the FS at very good prices. I feel I'm at the point where there's no need to get another dac. Although at 1k for refurbished I would jump on that in a heartbeat if I was in the market for one.