The iPad mini might be Apple's response to mostly fill the gap. The device can run phone apps without having the features of calling/texting.
The tablet also has more educational value as it supports handwriting and drawing, though it comes at the cost of not being pocket-size (adding inconvenience for users who just want to listen to music).
The regular "iPad" is more similar. Low priced model that lags behind the design and power of the flagship models. Starts at $329 vs $500 if you don't mind the big bezels, lightning port, and A13 processor with 3GB RAM.
Mini has the small bezels, USB-C port, supports the magnetically charged stylus, and has an A15 with 4 GB RAM, so it's priced more in line with the iPad Air even though it's the small one.
I used to have an iPad Mini, I think 3? Whichever model was before it got Touch ID. Back then it was a smaller and cheaper version of the normal iPad, more recently it's moved to the middle of the line (but below the "Pro" versions).
I just realized the iPad mini I still use doesn’t have Touch ID. I have an iPad mini 3. It’s slow on the last OS it can be on, iOS 12. I use it because a jailbreak tweak that can last.fm scrobble (tracks listening/viewing history) works on older devices like that one.
Just went and checked, the Mini 2 didn't have Touch ID, the 3 added it but changed pretty much nothing else.
I think what I had was a 2 purchased after the 3 came out, someplace was clearing them out for around $150 off even though it was practically the same device except it took half a second longer to unlock. Pretty good deal, eventually got demoted to kitchen recipe screen.
The iPad mini costs more than an iPhone SE. it’s not that small either so if it isn’t going to be in your pocket, an iPad is over $100 cheaper.
I think the iPad Mini makes sense as a product line in general. Which is being a smaller screen (and thus cheaper) iPad Air. It does work as an option, but so do iPads.
Or maybe they see that as belonging to the iPad mini’s purpose.