So many people saying the mini small size wasn’t popular, and whilst I concede the device DID fail I don’t think it was the form factor that killed it. It is the fact that not only it was smaller, and hence you’d expect to cost less, but it didn’t, it was expensive. It was a budget (non-Pro) model and yet STILL was almost as, if not more expensive than large models of the previous year - which were still on sale. People might be happy with a small phone, but they’re going to expect to pay the small phone price. Apple priced it at a point that it got cannibalised. And we can see the same thing happening to the larger models now too, which are also being cannibalised by previous generation, even though they are not tiny at all.
Perhaps you don't feel the price difference was enough but the mini did cost less. When the 13 mini launched, it started at $729 compared to $829 for the "regular" 13. Today, the 13 mini starts at $629 compared to $729 for the regular 13.
If we strictly use display size as a guide for pricing, the 13 mini's screen size is about 88.5% (5.4" versus 6.1") that of the regular 13. As I mentioned above, the regular 13's starting launch price was $829 and therefore 88.5% of that would be just under $734 which is very close to the 13 mini's $729 starting launch price.
As far as comparing different model generations, you could also go the other way and conclude that the 13 mini is not just $100 less but $200 less than the regular 14.