The technologies behind thermal cameras are very different because they need to be sensitive to wavelengths 10x longer than visible light (the silicon in CMOS is basically completely insensitive to light above 2 um, whereas thermal cameras need to image at ~10 um). The pixels are effectively microbolometers and rely on more exotic materials like Germanium.

A major limiting factor in camera sensor resolution is signal to noise ratio. It is well known that if you bump up the "ISO" (light sensitivity) to make photographs at night, you see more noise. The higher the sensor resolution, the smaller each photosite and therefore the less signal (fewer photons) captured in the short time of one exposure.

Larger sensors can solve this problem but these are CMOS devices whose cost increases superlinearly with area (like microprocessors, see die yield). Most customers won't accept dead pixels.

Economics is also a major enabler of kilobuck 50 MP visible light cameras, miracles though they are. Industrial users aren't going to re-buy all their cameras every few years like DSLR users do.

Mike did a real teardown on a Flir E4 many years ago, and saw (with an oscilloscope), even on the cheap camera with the low resolution, the chip has the full resolution. I think one week later the camera was hacked.

https://www.youtube.com/watch?v=NtqUE67BUDI

The major market so far seems to have been tactical/military, so they have focused on framerates rather than resolution. And then the US blocked high framerates for civilian use...

(edit: the US blocked civilian exports.)

As for the price per pixel: I don't know from memory.