When the films were in two parts, the AUJ portion had twelve plastic kits for it's portion of releases (perhaps intending to release one a month, who knows). Plastic kits take a lot of time to develop, and need to be made at least three months ahead of release for WD purposes, and also extra time for WB approval process. These releases would have been planned well in advance - this is why DoS didn't have any 'new' plastic kits. Not enough time to do Laketown guard in plastic (sadly), and their role was originally much smaller, so resin was a suitable initial choice.
It makes sense that GW sought parity between the two films - hence twelve kits and a terrain piece. The dragon is certainly one of these kits, and the laketown terrain is certainly the terrain kit (think about it - what purpose would laketown terrain serve? The bolg attack was added late in pickups, it never even got a look in on the DoS Sourcebook. AUJ had a big 'setpiece' table display - goblin town. There and Back Again seems to have had the Dragon attack as it's display board.)
Now I admit that it's just a guess that GW sought equal releases for each film. They may have wanted more, or less, for the second film. Ultimately very little of DoS's second half was suitable for release - they were stretching themselves to even include the Gundabad Orcs, and the plastic kits were perhaps dedicated BoFA releases.
Since AUJ finished releasing we've seen some delayed kits released (mirkwood) and a handful of resin models. The Perry Twins only left GW in June/July - they've been secreted away doing something for almost two years. In that time, in their spare time they have produced a fair old number plastic kits and metal relaeses for Perry miniatures - one can only imagine the amount of work they can complete working 9-5 Mon-Fri.
So I think we're going to do alight - the vast majority of things in the movies seen thus far, that've not been more suitable for TBoTFA, have been released (in fact I struggle to think of an example that hasn't). Including a breakdancing thranduil. GW isn't going to fob off the Hobbit until it's brought in every penny it can, or they'd have done it with DoS. They certainly aren't going to throw out plastic kits where the work has been completed over a year ago.
