As opposed to the BRD, where for example the "Auswärtiges Amt" had more ex NSDAP party members after 1945 than before?
There definitely was denazification in the east, but the totalitarian enclosed and literally walled of mindset did not help with creating an open mind towards the world. Add to that high unemployment and poverty after 1990 and you get the usual extremists on both sides of the spectrum.
https://en.wikipedia.org/wiki/1990_German_federal_election
No radical party was of any significance. If they were all Nazis, why didn't the NPD have 20%?
You are the one who rewrites history.
They vote AfD because the traditional parties have failed them and keep doubling down. The AfD would probably also fail them if in power, but that is the nature of protest votes.
Same story in France where Le Pen is currently leading the polls.