One of the applications used in most Ubuntu-based distributions and in Ubuntu itself, the Startup Disk Creator, is practically useless because the bugs that are preventing it from running properly haven't been fixed in years.
If you try to use the Startup Disk Creator, also known under the name of usb-creator-gtk, you will probably fail. Most of the time, even when it’s used from a terminal, the application will crash without any errors, making it impossible to write Ubuntu images.
The tool has been included for years in Ubuntu and other Ubuntu-based distributions, but it doesn't work and it never has.
Some of the bugs in Launchpad regarding this particular package have been marked critical and ignored for years on end. Take a look at the huge list of bugs for just this one package, 313 to be more precise.
As it stands right now, Canonical should either drop this miserable excuse of a software, or talk with its maintainers and fix the problems. It's not normal to offer another LTS release with an application that doesn't really work.