Why is USB stick not booting to update BIOS? Is this possible?

I want to update the BIOS for a system. I downloaded the latest ISO of the BIOS directly from the system's manufacturer. I used Linux Mint's USB Image Writer to make a bootable USB stick of the ISO. It created an ISO 9660 filesystem image on the USB stick (which itself is a portable USB stick reader with a 4GB SD card inserted in it). I set the system to boot from USB first and to temporarily boot up using legacy CSM mode with Secure Boot disabled. The system would not, however, boot from the USB stick. I then switched to UEFI boot mode, but the system still would not boot from the USB stick.

Question by Amazon Dies In Darkness on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.