I don't know of any more or less famous person, who could've ended the Dieter-Era at that time.
Dieter is commonly used as a nickname of
Dietrich - most Dieters I know are actually called "
Dietrich". So you could say, in a sense,
Dieter was popular before 1932.
I guess, it just came out of use, because it was associated with old people.
After the war - especially since the 60s - the type of names given to children changed. Names like
Heinrich,
Dietrich,
Friedrich,
Gustav ... that had been used for decades, vanished. New names appeared
Maybe the parents wanted to differentiate from their parents - the nazis.
Dieter actually was part of the top-100 until the late 60s, part of the top-200 until the late 70s - the time of the large movment among students:
https://en.wikipedia.org/wiki/West_German_student_movementThere was a rapid fall of the name around that time. This suits my explanation above.
I can't say for sure, though.