Why are degrees revoked due to data fabrication/manipulation only in specific fields? I read on the Internet that most degrees in psychology and medicine are revoked because of data manipulation/fabrication. In other areas like engineering, degree revocations only happen due to plagiarism.

How can data manipulation misconduct only be detected in medicine or psychology, but not in the other fields of investigation?
I think that part of what you see is due to the fact that in some fields it is more necessary to actually look for problems than in others. Thus, in medicine, for example, people's lives may depend on the accuracy of results, so people are more inclined to want to either investigate the accuracy of the claims or to replicate the studies. Faked data becomes obvious only if you look. If opioid research is faked, for example, bad things happen to a lot of people. When bad things happen, other people want to know why. 

In other fields, where the consequences may not be so dire, there is (a bit) less incentive to go looking for trouble. If few are looking, not much will be found. On the other hand, people who find themselves plagiarized are generally happy to raise the issue, but I think that happens in all fields, but is also fairly rare.