Because further investigation is dangerous. So you see a mass which has an a posteriori probability of being cancer of 1%, but the investigation causes serious complications in 2% of cases, then the decision to investigate is not clear cut. The additional information has not only not helped but has led to additional stress.
Not all further investigation needs to be surgical.
A mass that is found can be observed in decreasingly frequent ultrasounds or some other imaging and surgically investigated/removed only if found to be growing or passed a concerning size threshold.
A doctor jumping straight to invasive procedures seems to be a mix of poor risk management and rarity of this type of medical imaging.
My doctor for example, pointed out that actually in some East Asian countries, there are routine annual imaging tests done that pick up some of the types of cancer we do no screening for.
To me the reason we don't in US is simply how medical care is paid for - employer provided insurance, and some actuarial calculation that on the insured pool they'd spend more money on imaging than they'd save on high cost stage 4 cancer care. Personally I'm happy to advocate more for myself, even if it costs money.
