Microsoft’s support lifecycle policy. Because Windows 8.1 is in "End of Support" (EOL), the company no longer offers the tool via mainstream channels to encourage upgrades.
For the purpose of creating a USB drive or ISO for , select the second option: "Create installation media for another PC" . Click "Next." Media Creation Tool Windows 8.1 Pro 64 Bit
: If you already have the ISO file, you can create a bootable USB using command-line tools like DiskPart and Xcopy . Does Windows 8.1 have a media creation tool? Microsoft’s support lifecycle policy