VP9 and AV1 are less affected not because they're free and open source, but because they're backed by large-enough companies (Google) and a consortium that promised they won't claim royalties for the patents used in the formats. Companies outside Google or the consortium can still claim royalties, and indeed they do. See the Sisvel VP9/AV1 patent pool for an example of patent holders claiming royalties for technologies used in VP9 and AV1.