...that's because the PC file explorer is not an "app"; it has been there ever since Windows 98 (or even earlier), but modified with each OS version. Besides, what "capabilities" are you missing?
Copy - got that.
Move - got that.
View file info - got that.
Create new folder - got that.
Search - got that.
Besides, File Explorer isn't the only Windows 10 Mobile app out there. Generalizing the entire Windows 10 experience based on one app won't really be accurate, right?
On a side note, how's your Lumia 1020 performance going in the new build? Can you confirm the lauch time for the new Camera? Is it faster?