Why can't I make an audio album of family audio for Apple Books?

19,1 iMac, Monterey 12.1:

I have several audio recordings from family gatherings. I imported them into Apple Music, gave them one album title, assigned track numbers & titles. But when I drag the album to Apple Books I only get the first track of the album.

Why is this happening in Apple Books? It never used to be that way. I could always play all the tracks in Books from the Album.