Passive voice is for lab reports, research papers, similar scientific/engineering documentation, although I also see a lot of "we" used in papers, especially CS papers.
The use of active voice in scientific papers is an increasing trend. In the old days it was thought more scientifically appropriate to merely state that things were done without personalizing it, but gradually folks came to realise that scientific papers are hard enough to read already and that page after page of passive voice just makes it harder.
Well, I certainly agree that it's typically harder to write a long document in the passive voice. Describing what I did accurately and clearly is a big enough challenge without also having to contort everything into the passive voice.
