[metal_am]

Airport scanners are not CT. They will only give you one projection. I would also be willing to bet these CT machines can only scan a very small volume. Typically, they will rotate the sample, not the X-ray source and detector. I’d imagine some of the cost comes from being able to move the source and detector while keeping everything in alignment. (Disclaimer: My experience is secondhand with scanning metals)

[twbarr]

The passenger checkpoint devices are projection imaging, but they do use CT (with rotating source/detector, just like a medical CT) for checked bags. https://www.envimet.com/en/product/examiner-xlb/

[joshvm]

Newer ones are actually moving to CT. If you go through one of those security checkpoints, you don't need to take anything out of your bag. They were being used at some terminals at Heathrow - but confusingly not all. I think T2 has them, or at least were trialing them when I flew in September 2020. T5 definitely didn't in January.

[habi]

Nitpicking detail; the standard belt-scanners don't give you 'one' projection, but have (most probably) a linear detector with a (nearly linear) x-ray source pointed at, so they give you a slit-scan image, which is not one projection, but a veeeeery long image :)