I did this in class today, my answer was that the POWs had suffered enough in Russian camps, so Germans did not want them to be bothered/make them also feel harassed at home. What were German attitudes over denazification overall?
Source: Elizabeth Noelle and Erich Peter Neumann, eds., Jahrbuch der offentlichen Meinung, 1947-1955, Allensback 1956, p. 142.
edit: image link of source https://imgur.com/590Huhi
From the perspective of a source analysis, the problem seems to exist more in the image of Denazification rather than the actuality of it. In 1948, the question asked in the survey was about being harmed, only 16% agreeing could reflect the general loss in belief of the Nazi regime by this point. Many people lived for up to a year outside its borders before even the end of the war and many people stuck inside witnessed the destructiveness of the Nazi leaders, so they would likely have rethought their beliefs (if they had any sympathy in the first place).
As for the sudden supposed increase in people opposed to Denazification, I would suggest it is in the wording and supported by uncertainty that these numbers appear. This time, people are answering if they believe a very specific group should be subject to Denazification, a group that as you said had already been subject to much pain. There were also not many people left from these camps, I can't remember the exact numbers but according to The Forgotten Soldier by Guy Sajer, a large proportion had either died or never returned home. Many of these would also suffer from apathy towards the Nazi beliefs or have had time to reflect (re-education as the Soviets called it).
Finally, from the statistics at the bottom, people clearly had a lack of faith in either successful or the the program of Denazification. The largest increase was from the fear it was an occupying force projecting their power onto the Germans, while still a lower number than other groups, it symbolises a potential trend in attitude to the program as a whole. This is also supported by those selecting Don't Know, which further supports the idea of apathy towards the program (either there wasn't enough Nazi sentiment to be a threat or they simply did not see a point). Also those who just want to forget and move on potentially with Nazi-sympathetic family. Within this group is also those still holding Nazi sentiments or at least some level of nostalgia for the regime, who generally would oppose Denazification.
As a side note, I can't speak for the source creation as much of that is left off.