Call the deck zHidden instead, and it will sort to the bottom of your Decks list, out of your way.
This has been proposed a number of times over the years, in each of the apps. [For starters, see the list of “Related topics” at the bottom of this page].
One reason it is unlikely to be taken up is that the order of decks in the decks list matters to the scheduler that puts together your study session. Having invisible decks would create a lot of unexpected behaviors.
For another reason, I’ll just quote one of the developers –