The problem, that I see, is that having a retailer that isn't a relatively small business or, like ThinkGeek, bought out by some other party that refuses to sell emulation platforms would be helpful. Presumably some retailers are big enough that they might order 1000+ units in advance and take a chance on actual demand. At ~$150 It's also a little bit expensive as the market goes in my opinion. It was then and it probably still is.
If there is no lack of interest from end-users then why is there no apparent production? There's a chicken and egg situation if a retailer won't order any units without a guaranteed sale and therefore creates no listing and the interested party can't order because it's not possible to make an order.
Only one of the official sellers even has a page/listing (https://www.dragonbox.de/en/84-gcw-zero) and the rest either have no page (GWW) or their online stores are in limbo (Ithic, Extreme Hardware).
A few good, exclusive games for it would make a better case. It's true that a major part of the audience is interested in emulators, but the device is probably a hard sell otherwise and I'd bet on cheaper emulation/replica platforms.
I think it's a lack of marketing the product and showing potential resellers that this device is in high demand.
If you don't market the product properly their will never be a high demand, simply because too few people know about the device. So if you market the device properly and show your potential retailers the potential the device has and show them your device is in high demand and will definitely sell, they will order a lot more, allowing you to produce more.
Basically the lack of creating demand through marketing (except for the KickStarter event), the late delivery of a lot of KS units also negatively affects the device's popularity, decreasing demand even further, as well as retailers getting disappointed with orders not being delivered or delivered late, while they invested money.
In short: No demand, means no sellable product, ergo no one willing to sell your device.
That's the gist of it. Of course their are a lot of fine details in between, but I think the marketing plan for the device was very poorly designed resulting in low demand and therefore lack of retailers willing to sell.