Because you're not using the tool correctly. The Media Creation Tool is not used, in any way, to directly load Windows 10. It is used either to obtain the Windows 10 ISO file, which you then have to burn to bootable media - whether DVD or USB thumb drive - using a utility to do same, or to directly create a bootable USB thumb drive that can be used to install Windows 10 on a computer.
There are lots of tutorials on how to install Windows 10 from a USB thumb drive, provided you have a thumb drive that is *bootable* and contains the Windows 10 components on it this is a fairly straightforward process. The trickiest bit, generally, is rearranging your computer's boot order to boot from that drive as part of the install.
Brian AKA Bri the Tech Guy (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
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