For some, it's because of Roblox's audio permissions change that rolled out in around March. For the rest, it's because they're not meant to have audios.
We're working to restore audios all the time through our dedicated music production team, but this will take a while.
If the emote you’re doing triggers an “🔇 Audio Unavailable!” notification, that simply means we haven’t given the emote an audio. If it’s unintentional, we’ll fix it as soon as possible.
We’re unable to recover the original audios due to copyright concerns.