I don't recall attending or leading a prayer breakfast being mentioned as one of the duties of the president of the United States, as mentioned in Article II of the Constitution of the United States. Nor is it mentioned in any statute passed by Congress.
It wouldn't bother me if a president of the United States, Democratic, Republican, Green, Libertarian, or other, never attended a prayer breakfast. The president is the leader of a secular government.
It shouldn't matter if a president of the United States never entered a house of worship during his or her term of office, or entered once a year, or weekly. It is immaterial and irrelevant.