If you hadn't included the link to Macrumors, I'd have guess that the mini sells poorly because the iPhone SE is available and much cheaper. Personally I really surprised that the SE doesn't sell more.
>>mrweas+(OP)
Anecdotally, I wanted a Mini, but the lack of top-end cameras being available made me hesitant. I ended up buying a SE, since the neither phone was exactly what I wanted, but the SE was so much cheaper.