It's pretty difficult to click on a thing that is just in the border of the window. And what will be the problem if the Sidebar is put in the left and people click it accidentally? It only opens the window, it does not trigger any action which can affect the gameplay.
Right now is pretty inconvenient to have it in the same side as the inventory. Cause for example I play many time with the inventory open and I need to close it first, or move it away, and then I can see the Sidebar if I opened with F5.
All you have to do is moving it a few centimeters to the side, its not much of an inconvinience. Its just a matter of getting used to.
And infact, having it on the left side can have people accidentally deactivate or activate the anti experience.
And who knows which buttons we will add there in the future.