The main part he had trouble with was configuring the firmware to allow the installation, and then know about the new UEFI partition, and then forget about the no-longer-extant Windows boot partitions.
It wasn't obvious how to make that work even for me.
putting the ISO on the USB, telling the BIOS to boot from the USB, dealing with any random failures in grub or whatever, these are showstoppers for nontechnical people.
(actually the grub failures are a showstopper for me as well, I've never been able to figure out what you're meant to do if you boot up and get an error at that stage. I just re-roll with a different USB drive or distro or ISO-burning tool and cross my fingers)
also nontechnical ppl often will only dare use linux if they have windows as a fallback option, so they want to dual-boot. and setting up / maintaining a dual-boot system has its own set of failure modes.