Time was that Medium Format was a real thing. That was in the days of film. The canonical format was a square, 6cm on a side. There was also a bit of 6x7 running around and 6 by 4.5. The latter was, frankly, marginal. It was about not quite twice as big as 35mm (in linear dimensions), although of course the vendors touted its 3x area.
Surface area is all very well, but what really matters in linear dimensions. With linear dimensions 2x as big, you can enlarge 2x further. It is the linear dimensions which turn up in the diagrams which explain why focus drops away much more quickly with the larger formats, and so on. Obviously area and linear dimensions are inextricably intertwined, but quoting areas tends to obscure differences as well as making marginally larger formats look much bigger.
It is these linear dimensions that make the difference in the way larger formats look. The sharpness of focus drops off in such and such a way, there's probably something about how the lenses render out of focus material at that larger physical scale, I dunno. I am pretty sure that most of what you get from a 2x longer edge on the film or sensor can be obtained by opening up about 2 stops, but perhaps not quite all of it. In any case, you run out of stops to open up, quite quickly. Physics, it turns out, is not to be flouted so easily.
Enter the digital era.
We find medium format equipment vendors frankly scrambling. You simply cannot build chips anywhere near as big as the film sizes they were selling previously. The community of influencers making their living telling people to use Medium Format because it's what professionals use are likewise screwed. The systems are still present, but you simply can't make a sensor that's particularly big. There's just no way it's going to look like traditional medium format. Indeed, it's going to look a Great Deal like 35mm ("full frame").
And so you arrive at the present day when, essentially, you have a bunch of snake oil riding on the backs of what used to be a real difference. The largest available sensor is 100 mega pickles or whatever, and it's roughly the same size as what used to be the smallest medium format film. It's starting to look a little like medium format film. Introductory prices are in the $50,000 range. Systems affordable to all but the best off are still less than 2x the size of a full frame camera (linear dimensions), and even these are prohibitively spendy.
Yes, yes, you have much deeper color depth and more stops of dynamic range, maybe. Some of this is surely a sham. But everything modern digital medium format offers is small potatoes incremental stuff, stuff that that you can generally get out of the cheapest consumer grade stuff if you take a handful of exposures and use some software. That big leap from the 25mm by 35mm frame to the 60mm by 60mm is just not available. Of course there are subtle differences, and the enthusiasts have no trouble at all telling the difference until you blind the tests.
And yet the price differential is much bigger than it ever was.
As medium format lost ground on the technical side, it made up for it with hype and marketing. In order to cover the very real costs of what are, ultimately, enormous and expensive sensor chips, they've had to push prices through the roof. Digital Medium Format appears to be the exclusive domain of the well-heeled idiot.
A little poking around suggests that in 1976 you could get a basic 6x6 camera and standard lens for something in the general area of $1000 to $1500 new. In today's dollars, that's $4000 to $6000 or so. So, it's real money. It's also about half of what a 50 megapickle digital back will cost, all by itself. A digital back with a sensor that is 44mm by 33mm. A digital back that's going to make pictures that look a hell of a lot like those produced by a full frame camera opened up a stop.
Now, to be fair, digital MF has been leading the way. They always have more megapickles and bigger sensors. If you want to get out there on the bleeding edge, that's where you got to go. The trouble is that last year's products aren't really superior in any interesting way to this year's full frame products, and are still 3x as expensive. And, obviously, it's nobody's fault that there's no quantum leap to 60mm by 60mm available. Unlike film, where you can simply chop off pieces as big as you like, bigger sensors are arrived at in a series of small, painful, expensive, steps.
But that doesn't change that fact that these are expensive toys for wealthy nerds.