The big secret is that they could detect cancer very early in most people, but the health care companies don't want to pay for the screening. You can pay out of pocket for these procedures. I was told this by a cancer researcher
EDIT:
Adding these caveats:
1. There is a ton of nuance in the diagnosis, since most people have a small amount of cancer in their blood at all times
2. The screenings are 5-10k + follow up appointments to actually see if its real cancer
3. All in cost then could be much higher per person
4. These tests arent something that are currently produced to be used at mass scale
EDIT:
Adding these caveats:
1. There is a ton of nuance in the diagnosis, since most people have a small amount of cancer in their blood at all times
2. The screenings are 5-10k + follow up appointments to actually see if its real cancer
3. All in cost then could be much higher per person
4. These tests arent something that are currently produced to be used at mass scale