What is rare, uncommon, and common are decided on by the manufacture and not by demand per se. If they priced the miniatures based on production costs they would not have this issue.
Yes and no.
WotC/ WizKids have definitely gotten better at picking commons vs rares. They learned very quickly that mooks make good commons as you need lots, but elite named NPCs and solo monsters make better rares. So even if a mini could be cheap to make, if they’re not desirable in bulk they’re better as an uncommon.
It was always annoying to have a baggie of common figures that you only needed 1 or 2 of at a time.
Simmilarly, high complexity figures (beholders for one) need to be rare, as the many paint steps and details required necessitates a higher price. These have to be rare.
They do also bank on demand. Trusting desired figures will drive more sales. But generally they also at least try to keep those rares high quality as well.
But pricing individual figures doesn’t work as well. If you could buy singles at stores, people would buy fewer blind boxes and just buy the exact minis they want, and end up getting far fewer minis in total. Which means the price of all minis has to go up. A lot. And you have high demand minis regularly selling out.
If you want non-random minis you just have to go unpainted. (And even then, popular ones are always backordered.)
Look at the higher price-per-mini of the Pathfinder Iconic boxes. And even then, it’s banking on you buying 3-4 PCs you don’t want to get one you do.