I remember that after not reading any new Batman comics for a couple of years, I picked up the books again in the early 1970s and found that a lot had changed, while I wasn't looking, including the fact that Bruce was now called "The Batman." And this was lettered in a way that harkened back to the earlier lettering style in the 1940s. It was a way of signalling to the readers that the comics were going back to those pulpy stories of the early years for their inspiration.
It just seemed right that he should be called "The Batman." Why had that ever gone out of style in the first place? I guess, in the 1940s, they wanted to be more family friendly and calling him "Batman" made him more approachable and benign. But that's exactly why going back to "The Batman" made sense in the early 1970s, because they were restoring that sense of mystery and dread to the character.
Yet, as the 1970s wore on, "The Batman" was used less and less and it became "Batman" once again. And since then there have been times when "The Batman" has been used as a call back, like with the animated series, THE BATMAN (2004), and now with the new movie, THE BATMAN (2022). But the reason these usages stand out is because it's not the common usage--"Batman" is the norm. How come?