Android comes pre-installed on my device, with automatic security updates and manufacturer support for the likely lifetime of the device.

I’d definitely use a Linux PC if it came out of the box ready to go like that.

I mean, it doesn’t magically appear on the device. You pay for the installation, it’s just included in the price of the device (with Windows you also pay for the license key, by the way). There are companies that’ll install Linux for you. Hell, pay me $30 and cover shipping, I’ll gladly set you up with, I don’t know, Fedora and even add a timer with notifications that’ll nag you about package updates, just like Android does.

with Windows you also pay for the license key, by the way

Your computer’s price is often subsidized by the fact that the manufacturer has an agreement with Microslop to preinstall Windows on it.

Excuse me, they do what now? Do you have a source on this? Because I know of this little article, but that was quite a long time ago.
Dell goes Ubuntu; "Windows tax" is $50 according to pricing

Dell has released the configurations and pricing for their desktop Linux …

Ars Technica
I don’t think nowadays windows is subsidized. Sure, some manufacturers may recoup part of, or all the cost by pre installing crap ware, but those that allow choosing your OS usually give you a discount for removing Windows.
Who is the goverment paying to install Windows?
It used to be Norton antivirus or whoever that would pay have their shit software preinstalled.
I was looking at a thinkpad some months ago on their website and selecting Ubuntu from their options took off $160.

Yeah, I know that, the manufacturer has already installed the OS etc.

What I want is a warranty and guaranteed manufacturer support, rather than me needing to figure out how to fix it.

Outside of specialized B2B software, I never met a tech rep that would be helpful with an issue. Do you actually have experience where you’d call Google/Apple/Microslop and get help with their software? In Linux world, with many programs I can just go and nag the actual developer of the thing, which often works wonders.
I had a driver issue with my laptop which was causing the microphone to not work, not only was it fixed under warranty, but they sent a tech to where I was studying to fix it, rather than having to drop it off.