Well there's the rub, virtually nobody
is selling out-of-the-box Linux PCs. So, if Linux is being installed by the user, you're rolling the dice on how nicely it plays with your wireless, touchpad, graphics, sound, webcam/microphone, HiDPI screen and so on. "Probably" isn't good enough when the competition is guaranteed to work out of the box. And again, it needs to be guaranteed totally automatic; the population we're discussing won't be able to make the correct selection from a dropdown or install drivers manually (or have any clue what that means).
The problem with the GUIs I've seen for Network Manager is the same problem affecting nearly all Linux software, which is they're geared towards expert users. They expose too many configuration options to the user instead of hiding them in menus or preference panels. Experts like you or I see past all the noise and recognize the relevant bits. But a layman doesn't know what anything means or what's relevant, so they're likely to become stuck and confused.
Worse, many of the visible but probably-irrelevant options will prevent them from connecting to the internet if they're set to the wrong thing. The biggest part of idiot-proof UI/UX is looking at a "connect to a wireless network" modal and counting the number of ways it's possible to exit the modal without vs. with successfully connecting. You want all roads to lead to the happy path, even with Grandma rand() at the wheel.
Most Mac and Windows software could use improvement here too, although to a lesser extent, and same with iOS and Android but again to a lesser extent than with the desktop OSes.
Think of a person who leases a Camry. They like it because it's familiar and easy to drive, it meets all their needs more than adequately, and it has a low cost of ownership. If something goes wrong they bring it to the dealership and it's either covered under warranty, or, if not, they just pay whatever the cost is out-of-pocket. When their 2 years are up they lease another Camry.
One of the car blog Jalopnik's writers, Tavarish (https://kinja.com/apidaonline), doesn't know why anyone would want a Camry when they could have a 10-year-old European sports or luxury car at the bottom of its depreciation curve. The idea they're maintenance nightmares is a myth; he does all the maintenance himself, and finds like-new parts in junkyards instead of buying from the OEM, so they hardly cost him anything to own.
Obviously, Tavarish is an expert mechanic. He can replace a clutch or a turbocharger in his sleep, whereas so much as a fuse or a headlight is beyond the capabilities of our Camry lessee. We are experts. If our printer stops working we can recognize the issue, find and compile the community-supported open-source Epson 6000 SUX driver, and be on our merry way. Other people, who think a driver is a golf club or Morgan Freeman, just buy a new printer.