I dated a dentist for a while. She found (and filled) more cavities than any dentist prior or post. No profit motive. She was also a high achiever. I posit that they are seeing cavities, but there's a large and subjective gap between "we should do something about it now" and "it can wait a long time before we need to consider work." Some cavities are tiny and never grow with proper oral hygiene. The "correct" approach is probably to fill them because it arrests any future risk.