I’m not him, but now that I think about it, there is a tendency for many people to prefer the more generalized term.

Where scientists don’t tend to use the word scientist as much, I can’t recall ever seeing the term in a journal article for instance. (I don’t read many, but I’ll read an abstract here and there) I’m not sure why. I expect it’s some categorization thing, where not all scientists perform research, so researcher is the more precise term. I’m just guessing as to the reason though, I do not have a PhD.