Honestly it kinda feels like Apple didn't give the "mini" series a fair shot / set it up to fail.
The iPhone 12 mini, while really COOL, came out at a time when a lot of people had finally started voting with their wallet regarding smartphone battery life. I imagine the poor battery life put a lot of people off buying the phone and likely burned many who did. It honestly feels like when Apple decided to finally listen to those of who did want them to develop a new, small, flagship phone, they deluded themselves into thinking people wanted a smaller phone so bad they'd settle for a sub-par (compared to the rest of the lineup) product, and were then surprised no one bought...a sub par product.
The 13 mini is honestly what the 12 mini should have been from the start, rectifying its flaws and delivering an overall fantastic device. However, given that the 12 mini had been sub-par it had to combat the stigma from the 12 mini while also being, arguably, a bit overpriced in a market where people who weren't explicitly looking to pay a premium for a smaller size equate small with "budget."
While I'd personally love to see Apple continue to produce "flagship" minis I don't think its "viable" (in Tim Cook's mind, any other company would kill for the mini's sales figures.) I do think it would make a lot of sense to rework the mini into the SE's eventual redesign, either as the SE itself, or maybe as an SE mini. This would allow Apple to serve the "small phone" and "budget" audiences at the same time (while also aligning with the unfortunate market perception of smaller phones as "budget")
I also think one could posit an alternative theory as to why there's no iPhone 14 mini which is that the iPhone 14 just doesn't offer enough over the iPhone 13 to justify developing a "mini" version or that some of the key iPhone 14 features like a bigger camera sensor and satellite connectivity wouldn't physically fit in the mini chassis. If that were the case we could see an iPhone 15 mini once Apple has a new (full) process node (and a bunch of other tech) to play with. (I'm aware this is... unlikely but hey, one can dream right...)
Either way I'm personally really looking forward to picking up a 13 mini on sale this holiday season (or maybe next holiday season as my Xs is still more than fine and the 13 mini will be sticking around in the rotation this cycle,) got one for my partner last year and despite her initial reservations she loves it.