I find that younger, usuaty male, staff at some businesses sometimes call me sir. I take it as an attempt to behave respectfully.
I think there are some guys out there who like to be called sir, and may have made their kids call them sir, and have trained their kids to do so. Or in some cases, vestiges of that whole thing.
Of course it also happens in military and maritime traditions, and is a sign of training and recognition of one’s place in the chain of command, and part of a communication/training system/culture to have a clear and smooth hierarchy of authority in such an organization.
And that has its origins in previous eras social ranks and forms of address. Even 60–70 years ago in the USA, there was much more awareness and significance placed on “correct” forms of address. “Sir” dates back to the proper title used before the name of a knight (e.g. Sir Galahad).
In most modern cases, I think it communicates some degree of that “I am at your service” sentiment.