As someone who hires people in my own company and who asks this question the reason is quite different from your understanding.

I would hate to insult a candidate with an offer and always asks people to tell me how much they want to take the role.

Most people responds by saying "today I make xxx". And if they, as many people do, say "I don't know, it is hard for me to decide" I will ask them how much they make today and ask them if they feel satisfied with that.

To me it seems like 80% of candidates have a very hard time at negotiating salary because they really want the job. I will never, ever ask these things to try lowering the salary cost. I do ask these things to ensure a fair offer.

... but I guess it can be understood as you say it here as well. Never thought of that. That is valuable to know.