Their formula does not disable libdvdread support, but their build from source process fails to detect it if it is otherwise installed. A build from the vanill

Their formula does not disable libdvdread support, but their build from source process fails to detect it if it is otherwise installed. A build from the vanilla source tarball picks it up just fine. So this is not a "Homebrew decided to disable this option", it seems to be a "Homebrew's build process actively avoids searching for other installed software even when the authors of that underlying software enable support by default".