You are probably on to something there.This has nothing to do with preferences and all to do with marketing.
If the iPhone 12 mini was instead sold as the standard "iPhone 12" and then the 12 as a "12 Plus", imagine how sales would be different. Then take that and imagine that the hypothetical "12 Plus" got released 2 weeks later, giving the other an automatic selling advantage.
Not many are staying away from it because it's too small. It's about as large as the iPhone 6/7/8 which are considered normal-sized. The name "mini" is its biggest limitation.
I compared the 12 and 12 mini tempered glass I had laying around. The difference isn´t that big and most of it is height which on the 12 is just frustrating when handling it because you have to shift the phone in hand to pull down from the corners. Seriously considering flipping back to the mini and cope with images and videos feeling a bit too small, but having the benefits of one-handedness and managebility. It also feels more of a phone when used as one. 12 and upwards feels like holding a slab to your face.
Pricing is higher in EU than US, but I don´t care that much. The cost of a phone is very low when you considered all it can do and replace. I mean, not many years ago we bought compact cameras costing 500-800$ with a lot poorer images coming out of them and our paycheck was half of what it is today.