As the OP notes, they were still makinmg black and white movies into the 1960s. The Bedford Incident (1965) was b&w, and I don’t think it was for artistic reasons. Ditto The Train (1964) and King Rat (1965). Dr. Strangelove(1964) could as easily be b&w for commercial reasons, considering when it was made. I suspect that the subject matter tilted it towards b&w, too.
The first b&w movie I can recall seeing that was made that way for artistic reasons was Lenny (1974).
The Hustler is definately black and white for artistic reasons; lots of movies like that were.
Anybody know the actual cost factor of using black & white vs color film nowadays? I’m thinking Hollywood Shuffle, El Mariachi, and The Blair Witch Project are three recent examples of very low budget films shot in color.