I have always thought is was similar in meaning to ‘Think nothing of it.’
“My Pleasure” screams “I have been to a corpspeak seminar and drank deeply of the Flav-R-Aid”. It affirms in my mind that I am being “handled” and that any kindness that came through was insincere.
I’ve been doing telephone work for over 20 years. There have been times where I was strictly corporate and stiff, and other times where I was just me. Without exception, the conversations are more productive when I present myself as a real guy who knows what is what, and whose mission is to impart that knowledge to you. IME everyone from lawyers to meth heads are more willing to trust someone speaking in a vernacular tone than someone who sounds like they know the conversation is being recorded for training purposes.
I wonder why people get so ticked off by such minor variations from the expected, Emily Post-approved responses. It’s not the exact wording, but the tone of voice and facial expression that matters. Of the handful of languages I know sufficiently well to say “you’re welcome” in, there isn’t one that uses the literal translation of “you’re welcome”. Instead it might be “Of nothing!” or “Please, very!” or something else besides.
Similarly if I do favor for someone, and they say “Awesome!” or “Fantastic” or “Totes amazeballs!”* instead of the “required” thank-you. Interjections like “thank-you” and “you’re welcome” are just placeholders for a brief and polite interaction in the course of daily life.
*Not that I consider it likely that anyone will use this last expression to me.