How many people all over the world are going to sign up for Netflix just to watch this?
I imagine very few.
The existence of this 'documentary' was only confirmed last week. I doubt there was a mad rush to sign up in that time. Plus, unless you've got very 'niche' viewing interests, it's not the sort of thing people will watch for the viewing pleasure. It will be all about them making fools of themselves and spilling royal tea. That will be all over the web this time tomorrow. No need to sign up to watch it.
Plus, don't you still get a month free with NF? Even allowing for the fact that this pair's ability to capitalise on their dwindling royal connections seemingly knows no bounds, they surely can't get another series whining about the horrors of royal life, can they? It will be one and done. Surely.