Not a doctor, but to my understanding there are two main issues with CT scans in this context: the radiation from the scan itself, and the fact that it can lead to "incidental findings" which then might cause a cascade of other, more invasive tests with risks of their own.

CT scans are super valuable for all sorts of things, and the radiation dose/risk for an individual is small, but at a societal level using them freely as a "might as well" kind of test results in a lot of excess radiation exposure. This recent research suggests up to 5% of cancer diagnoses each year could be from CT scan radiation: https://www.ucsf.edu/news/2025/04/429791/popular-ct-scans-co...

The "incidental findings" side is an interesting dilemma: CT scans often reveal other stuff beyond what they were initially ordered for, but which can't be identified solely by the CT scan itself. So, if something looks a little weird on the CT scan it creates an imperative to figure out what it is, so there are additional tests, each of which carries its own risks and also consumes limited resources that might otherwise have been used for people with more definitively concerning findings. https://en.wikipedia.org/wiki/Incidental_imaging_finding