What was the reason for banning advertisement?
Religious TV advertizing is forbidden in Germany. It's just like that.
In Germany, there is a "Broadcasting Media State Treaty" that prohibits it. It is probably because the "traditional" churches, the Lutheran and Catholic churches (which are public corporations), help negotiate this treaty, although their influence has been steadily declining since the 1970s at the latest. Perhaps it's a way for them to keep competitors at bay.
It seems to be the case in America that certain people found religious communities in order to earn a living. I suspect that this behavior is considered "unethical" by the traditional churches and should be suppressed. In the meantime, however, there are programs of televangelists available here as well, programs of German-speaking preachers as well as international ones, so I don't really think the measure is appropriate.
In the 18th century, Germany had absolutism, in which the respective sovereign decided what religion his subjects should have. I suspect the attitude of the traditional churches is still a remnant of that authoritarianism.