There’s something wrong with the installer!
On a whim, I purchased Beat Essentials and ran into the same issue you’re having.
Here’s my workaround:
Inside the Installer window is an Additional Content folder that includes folders for Icons and VST Sound.
I navigated to the Groove Agent VST Sound folder: Mac HD>Library>Application Support>Steinberg>Content>Groove Agent>VST Sound
The two Beat Essentials VST Sound files in the installer were placed here as shown in the VST Sound attachment.
Next, I located the Groove Agent icons folder: Mac HD>Library>Application Support>Steinberg>Groove Agent Common>LIbraryInfo
The Beat Essentials icon was placed here. Groove Agent Common attachment
Beat Essentials now appear in the Groove Agent Instrument area. Selecting the icon will populate the presets area with Beat Essentials preset that match up with the list on the SB sight.
I did have some fun figuring this out, but a support link is at the bottom of the linked page on High Sierra.
