It would be much easier to obtain tissue from the breast than it is from the lung, and it would also be less dangerous. It
is not surprising to get an inconclusive biopsy report
for both breast and lung, but it
is easier to convince women with suspected breast cancer to undergo excision of areas involved as the surgery is easier and safer.
Of course, the first reason worsens the second reason. Since there is no screening, the mastery of the biopsy technique would naturally suffer.