As a hiring manager, how many times have you picked a candidate, called them, and they’ve decided against being hired by you? That’s you, having to go look for a shopping cart. Of course anyone who is going to write the note also said thanks in person. But if they write to remind you of the good points in their interview, maybe address some omission, you know they didn’t thank you to your face but mock you in private.
If someone gets an offer that meets their needs better (pay, interest, whatever), I just go to the next viable candidate from my pool. That’s hardly an imposition or a personal slight, and the potential for this to occur doesn’t change any of my behavior when hiring (other than, perhaps, trying to make a quicker offer for highly-talented candidates so I don’t lose them to a different opportunity).
