The secondary types, e.g. "Live", "Compilation", "DJ Mix" etc are not displayed in searches when the primary type is not specified/left blank/etc. (in fact it may not be displayed whenever the primary type is not "album") An increasing fraction of releases are created this way. Apparently the secondary types are regarded as more specific complete descriptions, possibly because the obvious default secondary type "studio" doesn't exist. The thinking appears to be that therefore an "album" is a "studio album" but choosing the secondary type "live" indicates a "live album", and similarly for any DJ-Mix or Compilation.
The primary type "Broadcast", and the secondary type "AudioBook" tend to reinforce the impression that a single selection from either the primary or secondary types is sufficient to completely describe a release.

Suggested remedies:

1) at data display, show the secondary type whenever one is present, instead of the current algorithm which appears to be if(ReleaseGroup.ePrimaryType == RELEASE_GROUP_PRIMARY_TYPE_ALBUM)

{...show secondary type...} use if(ReleaseGroup.ePrimaryType != NULL ){...show secondary type...}

2) at data entry require a primary type to be selected in order to select a secondary type

3) use a bot to update the database. for all existing releases with a non-musical secondary type set the primary type to "other". for all existing releases with a musical secondary type and a null primary type by selecting a primary type according to the minimum track count of any release in the group, primary type = single if tracks <=2, EP if tracks <=4, else album.

Suggested type reorganization to address the underlying problem;

4) Since MusicBrainz fundamentally presumes that entries are commercial music releases, let the primary types be the base categories of commercial music releases, and "other". Migrate the primary type "broadcast" to become a secondary type setting primary type other for existing entries. Create a matrix of contextual restrictions for secondary types. e.g. primary type must be "other" to select "Audiobook", "Interview", or "Spokenword". primary type must be album, ep, or single to select "Compilation" "DJ-mix" "remix" "mixtape" or "demo" , and so on.