Brian Gregory wrote:

They why are there special programs like Rufus that look in the ISO and
work out how to make a bootable USB stick from it?

Rufus is not required for Hybrids.

Linux Mint ISO and Ubuntu ISO are Hybrids with
legacy/UEFI capability when used optically,
as well as additional partitions for USB booting.

Simply do a sector by sector transfer of the ISO
to a USB stick, and it's ready to go.

The fact that Windows does a poor job of mounting
partitions ("for a look") is besides the point.
(Windows by default only sees one of the three partitions.)
If you want to look inside while the content is
on a USB key (sector-by-sector), try modern 7ZIP and
it will allow looking inside the USB stick.

The fun comes later, when you want to erase the USB
stick. Windows Diskpart is unlikely to support
"clean" on a USB stick. And this is because
a lot of USB sticks are saddled with the
wrong value of RMB bit.

*******

A *non-hybrid* disc may require Rufus or UnetBootin.
And there's probably still a few of those out there.

To put a *Windows* hybrid on a USB stick, use

Windows7-USB-DVD-Download-Tool.exe

and it works with installer DVDs from
Vista to Windows 10.

Paul