Another reason was the awful marketing of Apple here. People on the SE-2016 were already looking for an update. It was the SE-2020 in April 2020. People who bought this SE-2020 weren't ready to buy the 12-mini which got launched just 6 months later. Less than a year later the 13 mini got launched but that's still too soon to replace an SE-2020. Just 6 months later the SE-2022 got launched, again, too soon.
What does Apple think? People who buy a mini or an SE are not the typical "I want the latest model" buyers. They'll use it for as long as possible, at least 3 to 4 years. Launching 4 small phones in just two years just doesn't make sense from a marketing perspective. The user base got fragmented over 4 different models and apparently some braindead marketeer at Apple decided there's no market for the mini. And here we are, no more minis.