This reverts part of PR #15899 (commit dd6e3a0ece).
"Why is this even useful?": It's very useful for multi-disc playlists. Compare:
`mpv bd:///DISC{1..4}`
`mpv -\{ bd:// --bluray-device=DISC1 -\} -\{ bd:// --bluray-device=DISC2 -\} -\{ bd:// --bluray-device=DISC3 -\} -\{ bd:// --bluray-device=DISC4 -\}`