You realise that those are not your earnings. It says in analytics itself. Those are
estimated earnings.
Estimate
es·ti·mate
verb
ˈestəˌmāt/
- 1.
roughly calculate or judge the value, number, quantity, or extent of.
The number you see is just an approximation. Just as your views are subject to fluctuation (as Google regularly removes fraudulent views, mistaken views, etc) this and other factors also contribute to your estimated earnings changing.
You will almost certainly lose some of your initially predicted monthly earnings because many of the views on your videos will be found to be duplicates. A lot of times viewers refresh videos tons of times to reply to comments. Then there are your own views from replying to comments or editing or updating the video. These views don't make up a large part of your views on any given video, but over a total set of monthly views it can make a big difference when these views are eventually removed by the system, especially if these views were monetised.
If you look at the days during last month on which you had the most views, you'll notice those have dropped a little too.
Last month's earnings for me dropped $6 since the last time I checked them, but I also saw a decrease in views on some of my highest earning days, confirming what I said above about it simply being due to views being removed.