I don’t know of any Protestants who claim the Reformation was not about politics. In sixteenth century Europe, it was impossible to separate religion and politics because the Catholic Church had so embedded itself within the political fabric of the entire society.
The middle of Europe was a hodgepodge of different countries each ruled by a prince (most secular, some bishops) who claimed that they had the right to determine what religion would be practiced in their realm and would not accept interference in their internal affairs by a foreign power (i.e. the Papacy).
Why should it surprise anyone that this state of affairs would lead to religious conflict? On what grounds did the Catholic Church claim legal authority over the German princes? Who gave it legal authority over secular rulers? No one did, certainly not God. What were the theological grounds? It certainly is not a theological necessity for Europe’s governments to be politically beholden to the Catholic Church.
Why should anyone be surprised that given the chance the government of sovereign states would assert their sovereignty in any ways that make sense to them? Once the Protestant Reformation began, princes who were religiously sympathetic would no doubt recognize the political implications, but this only occurred in response to the religious momentum for Reform.
No. There were huge swaths of radical Reformers who had momentum and had no support from German princes at all. In fact, there were many Protestants who were persecuted by both Catholic and Protestant princes.