Burn playlist to disc - cannot set gap

Burning a playlist to an Audio CD, the "Gap Between Songs:" is set to a greyed-out "none" that cannot be selected or changed. (iTunes 12.7.1.14 on High Sierra Mac.)

It seems if this capability (to set a particular number of seconds gap for between all the songs) was simply being removed, that line about setting the gap between songs wouldn't even be there. Anybody know what's up?

I couldn't find any overall preference settings to change this... I also notice the "Include CD Text" isn't selectable.