Bootable CD/DVD - El Torito
A bootable CD or DVD is build up according to the El Torito standard. This means that the ISO9660 File System has an extension which provides information to a BIOS so that the BIOS knows where to boot from and what files to load from where. Bootable CDs or DVDs are a BIOS thing, once the OS is up and running the bootable structures are ignored.
It is not simply possible to copy a bootable floppy image onto CD or DVD and then hope the medium is now bootable. The File System really needs to know and needs to provide special structures and volume descriptors (in accordance with the El Torito standard).
If you want to create a bootable CD or DVD you need to use a mastering application that does it for you. E.g. in Nero or Easy CD Creator you can check an option to make a bootable CD/DVD and the application will then prompt you to insert a bootable floppy or use a bootable image.
FYI
http://www.nu2.nu/bootcd/
https://www.isobuster.com/tips/build_a_windows_xp-sp2_recovery_disc
IsoBuster can also deal with boot images that are not conform the specifications, made by mkisofs.
Additionally IsoBuster can also scan the boot image file to check if it contains a FAT file-system, and if it does, list those files and folders.