Currently when a release is removed its recordings, if any, get purged too. Under certain circumstances this won't happen:

• There are pending edits
• The recording is used by another release
• It was added as standalone recording (formerly non-album track)
• There are relationships on the recording

The most common reasons based on my observations as a voter are the presence of relationships or usage on another release.

The former is a constant cause of follow-up edits to remove those orphaned recordings one by one.
Especially playlists added as release (which are generally disallowed) with many tracks can be quite the chore to cleanup:

• https://musicbrainz.org/edit/80817391
• https://musicbrainz.org/edit/80819178
• https://musicbrainz.org/edit/80865519

To make life of editors less miserable I'd suggest to provide an option that will automatically enter edits to remove all recording relationships before the release removal is queued to allow ModBot purging affected recordings once the release is actually removed.

Ideally an edit note linking to the relationship removals is also automatically added to the "remove release" edit so others can more easily vote on those too.

A similar problem poses the orphaning of recordings via "edit medium" edits like https://musicbrainz.org/edit/77555091