I think what happened here is that the target audience are people that do not feel pressure to upgrade to the latest mini every year. They do not look to have the lastest-shiniest-ohlookAI-snapdraxxon22pro phone. Just a phone that is a bit cheaper but gets the job done.

Why would you go from 12 mini to 13 mini, or to the concurrently released SEs if your phone still works?

I am also still holding on to my 13 mini. I would not have upgraded to the 14, 15 or 16mini even if they existed. I will upgrade at some point, and that point is when it either dies, or important apps stop working on the last iOS version supported by the hardware.