Welcome to the Strelets Forum. Please feel free to discuss any aspect of 1/72 scale plastic figures, not simply Strelets. If you have any questions about our products then we will answer them here.
Plenty of mainstream WWII German afv subjects for Dragon to do like the Panzer I or II for example. I suppose people choose obscure models because they are attractive and attract those who are fed up with doing yet another Tiger I at Kursk.
The other major point was about quality. The donkey would sell well if it was well sculpted and designed etc. The Arms series has the potential to be attractive but they have to compare with HaT (not the polyethylene ones), Ace and others in white metal and resin. No reason to assume at this stage that they wont as they haven't been introduced yet( they may better them). British WWI Heavy Artillery is not exactly mainstream so they are being adventurous with these. Proof of this would be, as you state, they haven't been attempted before in plastic.
I collect the models and I am not really interested in what sells well. It has no effect on my choice. Furthermore, I haven't a clue what sells well. Things that I consider to be crude, old fashioned, etc just fly off the shelves. There is no accounting for taste or lack of it.
I realise that a manufacturer, no matter how philanthropic, does regard sales as a very important factor. They are taking the risks with their money. If Strelets want to make plastic bath toys for the under fives because that gives a better return- OK by me. I get the feeling that Strelets enjoy what they are doing and would probably seek a compromise that combines a measure of commercial success with their undeniable enthusiasm for the hobby. In the end, only they know where to draw the line.