It's done that way to prevent bricked TVs.

That said, don't stick large USB sticks in this update. Try 4 or 8GB sticks.

Remember that I am not Samsung support but here's what I run into on this issue.
1. The update was not for your model.
2. The flash drive is too big, unsupported format.
3. The owner didn't quite follow the install instructions.

For example this one tells me to place the downloaded.exe file on the USB stick and run it there then for the target use the root folder of the USB stick. Extracting to say your hard disk could have us get into trouble.