Why do PC games use anything besides FLAC?

I don't understand this. PC games use either uncompressed WAV (usually in a lower quality 22050 Hz or if we are lucky 44100 Hz) or low bitrate mp3s for the sounds or game dialog. Why not use 44100 hz FLAC files instead? It's an open format, and unlike mp3, you don't have to license a codec to decode the audio. DUH! Not only that, but it's CD quality audio at half of the filesize. You could encode the sounds, dialog, and music all to FLAC, and not worry about decoding mp3s, or have low quality audio. Why do anything else?