I was recently looking at the rates of PhD revocations of people who were found to have plagiarized large portions of their PhD theses by Vroniplag, and it isn't that high.
Most people that were found by sites like Vroniplag whose PhDs weren't revoked are either established professors or are working outside of academia so it's kind of understandable that their PhDs weren't taken.
But there seem to be instances where someone plagiarized portions of their thesis and they are still promoted by their Universities and given funding.
Why is PhD thesis plagiarism forgiven in some instances by academia?