Cannot select multiple files and change Media Kind to "Audiobooks"

I ripped a set of Audiobook CDs to iTunes 12.9.4.94.

The audiobook files are in diff format on the CDs.

My import setting is AAC Encoder.

The Info tab for the import Audiobook file in iTunes, it shows as "AAC audio file" (Info > File).

In its folder in iTunes Media directory, the file is m4a format.

The only way I can change the Media Kind to "Audiobooks" is by changing it for each file individually via "Info".

Based on this information, why can't I just select either the album, or select all the tracks, and change Media Kind through Info? The only setting there when I select multiple tracks is "Music".

I am running macOS Mojave Version 10.14.4