>I don't know why they wouldn't be able to install it themselves, tbh.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.
EDIT: the dumbest one I ran into was when I just couldn't figure out how to get into the BIOS. there wasn't any splash screen like you usually get where it says "press F{n}" (and why the fuck isn't that standardized anyway?).
eventually I figured out it was because the monitor wasn't turning on quick enough to show the motherboard splash screen, so the system had already started the windows boot process by the time I got to see anything. I had to look up the right key for the motherboard online, and then press it blindly the next time I booted.
EDIT: also doing this kind of stuff assumes you have another machine handy. you can use it as a "lifeboat" for your files, you can use it to burn USBs, look up documentation and so on. technical people tend to have a bunch of old machines lying around they can use in a pinch. but nontechnical people tend to only have one desktop/laptop. if they have anything else it's probably a phone or a tablet. if you only have one machine and you screw something up so you can't even boot, you're stuck in a catch-22. and then you need to take it to a PC repair place, and they'll just reinstall windows for you.