The Mini was supposed to be the "switch to mac" entry level desktop. Any easy way to go mac with your existing display and peripherals. Cost effective enough to get people into the ecosystem with the potential for their next upgrade to be a more fully featured mac.
The problem is it hasn't really fit in its place for a while.
The problem is, I'm not sure that place even exists any more - most "mainstream" users now want laptops, don't necessarily have displays to re-use (and if they do, they're mostly 1080p - yuk!)... and having that existing display is pretty vitally important because if you (a) want a decent display and (b) don't mind an all-in-one then the iMac is a night-and-day better deal, even by the time you've added $200 for an SSD (...and upgrading the Mini to a 256GB SSD costs the same).
The people looking for a headless desktop these days are more likely to be "power user" types - and the Mini's weak spot is that it needs an eGPU to smoothly drive anything more "power user" than a single 4k display, even for 2D work if you need to use scaled resolutions (which you probably do if you want 27" displays with sensible UI sizes). So, that's adding a few hundred bucks to the cost of the GPU for an enclosure (more if you want to use a Thunderbolt display so your only option is one of the Black Magic non-upgradeable eGPUs), a PCIe bottleneck between CPU and GPU, a list of caveats about eGPU support in various applications, and an extra box, cables and wall-wart. Sorry guys - eGPUs are an interesting possibility for laptops (and, maybe, a couple of years hence might give your iMac a few more years of service), but if you need one for a desktop on day one then something is wrong. Sure, the previous Mini hasn't had a discrete GPU since the G4 days - but people weren't plugging them into 4k+ displays, either.
The new Mini seems to have been tailor made for people running Mac Mini co-hosting services (a thing, but kinda niche) or the remaining few who desperately need a MacOS server machine.
The "switch to" Mac has long been the "classic" MacBook Air which has now gone - the recent price cut on the new model has helped, but its still psychologically on the wrong side of $1000.