It is not an exclusive focus on deaths, it is on all cancers and they did not spike as claimed by more pessimistic models. There were a few slight increases (mostly in thyroid cancer) but also a lot more testing being done that makes it a bit harder to normalize the statistics -- this may also have dropped the death rate slightly, as cancers caught early due to increased testing are more likely to be treatable.

Do you mean the number of death because of Tchernobyl is negative (less death than if Tchernobyl did not occur) ?

No, I am suggesting that part of the reason the death rate is much lower than predicted is that the testing rate has gone way up (and stayed up as testing became better and cheaper) and treatments have improved significantly, so incidences of cancer that might have been discovered late with few treatment options in the 90s are now detected early and treated as a chronic condition. More deaths overall, but a lot less than what was expected.

If you live in the fallout region then you are going to be placed in a high-risk category and are going to be watched more closely for cancer than the general population. By observing something we change it.

Most of the cancer treatments that make your life hell aren't commonly used on thyroid cancer. Generally you have part of the thyroid removed, and quite often it can safely be ignored with no harm done to the patient.