Please see this feature request in the Tails repository > Local storage 
devices displayed- Tails DVD no admin 
(
https://labs.riseup.net/code/issues/9554) where intrigeri suggested 
raising this issue on the mailing list.
The basic premise being that hiding the internal drives in working in 
what I call "safe mode" (booting with no admin privileges) to be more 
consistent with Tails  goals and objectives of consistensy than it is to 
show them.
Since without root login, access to them is denied it is pointless to 
show them in the file manager and in the Disk Utility. In response to my 
suggestion intrigeri rephrases it in his own words as:
"I can see your consistency point, that I would rephrase in my own words 
as "one should not even see what they won't be able to access anyway"; 
when I zoom in on it, it totally makes sense to me -- thanks for 
clarifying."
Not having any experience in coding myself, I am calling any interested 
parties who feel this to be a worthwile and valuable endeavour to please 
take it on and to implement and maintain this feature.
Thanks in advance.
Cheers.