I’m not sure what the general case looks like, but the professors who I have worked with (who all have the characteristic that they do applied-ish research at a top research university) are both constantly barraged by more e-mails than they can possibly respond to. I suspect that as a result they limit communication to sources that they know will be fruitful.
Other professors in more theoretical fields (like pure math) don’t seem to have this problem, so I’m not sure why they don’t do what you suggest (although some of them do). And I am not sure that all professors run into the same problem as I have described, even in applied fields.
I’m not sure what the general case looks like, but the professors who I have worked with (who all have the characteristic that they do applied-ish research at a top research university) are both constantly barraged by more e-mails than they can possibly respond to. I suspect that as a result they limit communication to sources that they know will be fruitful.
Other professors in more theoretical fields (like pure math) don’t seem to have this problem, so I’m not sure why they don’t do what you suggest (although some of them do). And I am not sure that all professors run into the same problem as I have described, even in applied fields.