The
Nazis campaigned to kill
entartete Kunst; like the
communists, they considered art as an instrument to build a pure, proper, prosperous society full of
upstanding citizens. This meant that critical, self-mocking, or experimental art was out of the question. Naturally this affected musical life, by favouring mainstream music over experimental, highbrow stuff.
Out of the same fear of the unfamiliar, the Nazis also campaigned against persons of (originally) foreign descent, or with unconventional habits, such as Jews, gypsies, gay men, etc. - this had a huge impact on mainstream popular music.
One example: one of the most popular musical groups of the time, a close harmony sextet called the Comedian Harmonists, were forced to replace three of their six singers for no other reason than their being Jewish.
Another example: the most popular Dutch singer, Louis Davids, was exterminated in a concentration camp, while his songwriter, Jacques van Tol, actively collaborated with the nazi occupiers.
Discrimination wasn't covered up like it is today, it happened in the light of the public eye, accompanied by ferocious propaganda campaigns on the radio and on posters, calling on people to betray their friends in the name of a pure, healthy society. It affected all aspects of public and private life.
During the war, American popular music was totally banned.
All of this created a strong resentment towards German popular music that lasts to this day.