The Need for Thank You

In the HBR:   In a long career, before search became common, and I had become a rumored expert, I was often asked to do a simple online search.  Later their admins would be trained.   I responded quickly in one case, though it was not my job.   No thank you.  A week or so later I made a point of asking if they had received my note.  Again, just a few lines.   They did respond to that, saying that they had received my answer.  But still no thank you.  Simple thing I will not forget.