Visible wavelength cameras rely on relatively cheap CMOS sensors. CMOS processes have been squeezed for efficiency for decades to make, for example cheap DRAM.

Visible wavelength cameras rely on relatively cheap CMOS sensors. CMOS processes have been squeezed for efficiency for decades to make, for example cheap DRAM. 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.