Not sure that completely addresses the parent comment's point. Glass is definitely expensive for good reasons (watch some YouTube videos on optical lens manufacturing to see why), but even just a camera body for something like an EOS 6D is still $1000. The sensors can't be that much, full-frame or no, so where is the added cost coming from? Certainly not software or on-board processors. To the parent comment's point, you can get a full-blown flagship smartphone with a 6 inch high resolution screen you can actually use and a good amount of memory baked in for that price.
It functions like an instrument that is designed to be used. Treated with reasonable care, from -30C to 100%-humidity-condensing conditions at the freezing point, it has consistently gotten the job done. It is compatible with a huge range of glass, and it all works. The interface stays out of the way -- when I'm making images, I'm never worried about the camera, just the photography.
When I'm working, the camera is always powered on. The battery lasts for weeks in that mode, yet when I depress the shutter halfway, it begins to lock focus in tens of milliseconds. With gloves on.
When these cameras are released, there are rarely, if ever, hardware revisions. They work that well on the day that they are shipped to the first consumers.
For me, the cost (and the value) is in the R&D and the ecosystem.
There are a lot of mechanical controls on DSLRs, and they see heavy use over long periods of time. Building those to withstand hundreds of thousands of operations, and making them dust and water sealed is probably not inexpensive.
The shutter for a typical DSLR can be expected to last for 100,000 shots, if not longer, while opening and closing in 1/8000th of a second. It's impressive engineering.
