I think you're mistaken. Just googling why use open source software and the results have a lot of information about security and very little about privacy. I don't think open source is inherently more private then closed source software. Yes there the community has some privacy minded leanings, but that won't stop any given open source project from leveraging and selling user dataI think there is a confusion. People prefer FOSS for privacy reasons.
Google's AI generated answer doesn't mention privacy at all
Most of the links I found on the front page of google fail top mention privacy at all. Seems like people in justifying open source and talking about open source don't seem to mention privacy as a major reason