It's likely more than that. Chernobyl had a great impact on people's idea of nuclear. Also its damage, when occurring, is done in a spectacular way by something invisible. Radiation poisoning is dramatic, horrific and you can't see, smell or feel. That scares the living hell out of most people and the fact that is statistically unlikely becomes irrelevant as soon as it becomes an irrational fear.
There are things that cause more deaths by cancer, slowly and steadily, that don't (or didn't) scare anyone - tobacco was an example. Junk food may be another.
I don't know if the transition was respectful in what regards Dan, but it sure was not respectful towards the listeners.
As you, I also feel he's free to move his show wherever he wants, but I also thing he owes his listeners an explanation, or at least a comment. 5by5 was the house we visited to listen to John (with Dan) and we show up and he's not there. A mere link on his website, with no explanation, is, in my opinion, rather distasteful. I haven't heard the new episode until the end, so I don't know if he makes any comment at the end. But certainly there's no explanation or introduction. Even if they parted ways in an unfriendly fashion, he still owes a lot to Benjamin.
Finally, he's an awful Sponsor message reader. Poor Piezo.
There are things that cause more deaths by cancer, slowly and steadily, that don't (or didn't) scare anyone - tobacco was an example. Junk food may be another.