I know I can format Bootable USB drives with gparted or software like that. I do it every time I need to.
But I want to know why nautilus can not format that? Is there any logic behind it?
I searched many sites but the only thing I found was How to format it with gparted or software like that.
Nautilus uses some tools under the hood, and one of those tools may have problems with some partition tables and or file systems.
It is a good idea to use a dedicated tool like gparted to create or edit the partition table and file systems (alias formating).
Some versions of gparted has problems with the iso 9660 file system, that you get, when you clone an Ubuntu iso file to a USB pendrive or memory card. When that happens you can use mkusb to wipe the first megabyte or restore it to a standard storage device,
help.ubuntu.com/community/mkusb