I don't think only the size has been the reason for the poor sales. Yes, everyone here in Macrumor's forums knows that the difference between regular/mini is only the size and battery, but normal people who are not into technology may not know that. The "Mini" name may have led people to believe that it was a "downgraded model" - also because the price was a bit less, it then made them choose the regular model because they were afraid to buy something that wasn't good enough, and when the price difference had been so small, it was a no brainer.
Apple should have launched iPhone 12/13 without using different names like Mini. But quite simply launched iPhone 13, same phone, choose between 2 sizes.
I saw it coming. That's why I replaced my iPhone 13 Mini, which I've had since release, with a brand new one for approx. 1 month ago when there was a good offer on it.
The iPhone Mini is a perfect phone for those who understand how devices "should" be used. An iPhone must be easy to carry in your pocket, it must handle the day's quick tasks. Reading an SMS, replying to a quick email, searching for information on the web, listening to music and making calls, the iPhone Mini is perfect for that. You should not watch movies or play "big" games on a phone. Movies must be watched on a large TV with surround sound. Work must be done on a Mac, and entertainment and light work is done on the couch with an iPad in hand.
If you choose to do everything on a phone, I understand that you don't choose an iPhone Mini.
RIP iPhone Mini. I hope you will be resurrected in a later version, and preferably with Dynamic Island aned a"matte glass" back, like on the Pro models. It's also perfectly okay if you come back as the new iPhone SE 4th gen.