So I'm aware that there are a small handful of drifter types that still occupy the territory around Chernobyl, but the area itself is by and large permanently deserted. Why didn't the Japanese avoid repopulating the blast sites of Hiroshima and Nagasaki in the aftermath to avoid radiation contamination? Or why didn't people move away permanently?
u/restricteddata discusses this here, https://www.reddit.com/r/AskHistorians/comments/f4llcz/were_there_any_longterm_issues_with_lingering/
And there they link to another answer from u/danegeld87 dealing with the cleanup in the aftermath:
Long story short, the air burst fission bombs did not produce nearly as much long term radiation effects as things like a melting down nuclear reactor or a hydrogen bomb.
My apologies to the mods if I'm not allowed to direct you to answers outside of this sub, but this is a question in r/askscience about the differences between a nuclear plant disaster and a nuclear bomb going off, which will answer the practical side of your question.
The one thing I would add to the older links already posted, in response to the specific question about "drifter types": the reason people don't live near Chernobyl is because the Ukrainian government has made it illegal to do so, because it is contaminated. There have been people working at the Chernobyl Nuclear Power Plant since its accident. You could, prior to the current war, visit the plant as part of formal tours. (I was slated to do so in March 2020, but had to cancel because of the COVID outbreak. I thought, maybe I'll be able to do it next year... and now that seems very hard to imagine. Sigh.)
The people who have moved back to Pripyat that I know about are less "drifter types" and more "elderly former residents." There are many who are famously old women — babushkas. Their general attitude is that they are old and don't care about the contamination. The Ukrainian government apparently is willing to turn a blind eye. From a health perspective, it doesn't matter very much. The levels of radioactive contamination are such that living there only increases your total radioactivity a little bit. That little bit can, over time, add up to a statistical increase in your lifetime cancer risk, and in a statistical increase in a risk of birth defects. However if you are already 70 years old, you are probably not going to measurably change your cause or time of death by moving there: it can take decades for cancers from low-levels of radioactivity to develop, if they do develop at all. And even if they do get cancer, the number of people is so low, and the population so old, that it won't possible to tell if the rate of cancer is much in "excess" of what would happen anyway. You are only talking about increasing their cancer risk by a few percentage points; in a small population, that data will just blend in with the "noise."
Now, if a large number of people moved back, especially young people (who have those decades to develop the cancers) and pregnant women, you would expect to see an increase in "excess" cancers and birth defects above what normally occurs. The larger the population, the larger the "excess." So from a public health perspective, banning people from living there is a good idea, even if the individual risk is still objectively small. But if a few old people move back, it doesn't really hurt anything.
The bombs dropped on Hiroshima and Nagasaki had far less radioactive byproducts in them than were released by Chernobyl. Each of the bombs only fissioned about 1 kg of fuel, so they only produced around 1 kg of the really nasty fission products that account for most worrisome radioactive contamination. Chernobyl, by contrast, released about 200 kg of fission products, along with a lot of other nasties from deep inside the reactor, which was at the end of its fuel cycle and in its nastiest shape, radiologically. (A nuclear reactor like Chernobyl releases, over the course of a fuel cycle, much more energy than the bombs at Hiroshima and Nagasaki. It just does so at a lower and constant rate over a longer period of time.) Additionally, the Chernobyl fallout went up and came down relatively quickly, so a lot of the area immediately downwind of the reactor got a very high load of the fission products. At Hiroshima and Nagasaki, the bombs were detonated high-enough in the air that their fission products did not come immediately down again, had time to disperse and "cool off" (the stuff with short half-lives could decay before coming down), and so was essentially diluted. As a consequence, while both Hiroshima and Nagasaki got a tremendous amount of radiation in the initial attack, they didn't get very much long-term contamination. Essentially all of the radiation-related injuries at Hiroshima and Nagasaki are attributed to the initial blast of radiation (and maybe some of the short-lived activity caused by neutron activation in the immediate blast area, but even that is hard to control for in the data).