Comment by Zak

I suspect the iPhone Mini didn't sell well for reasons beyond people generally preferring larger phones, and suspect it might sell better today.

The biggest issue is that it was introduced in 2020 when many people were in lockdowns. A phone's portability was not as important, and people mainly using their phone at home on the couch likely preferred large screens more than usual.

The second issue is that the screens used slow pulse width modulation for dimming and could appear flickery for some users.

Finally, battery life was uncompetitive. Sony Xperia Compact models introduced years earlier had larger batteries. My guess is accepting a tiny bit more thickness would solve this problem.