Time is money- plenty of people would trade $200 for not having to spend time doing that. That's the sort of thing that's really fun and cool and interesting if someone's a hobbyist and/or student and/or in the larval hacker stage, but at some point in life after spending decades having to make sure their hardware is supported by Linux/FreeBSD/whatever, the bloom can come off that rose pretty hard and it's a blessing to just give someone money to worry about something you don't want (or don't have the time) to spend time doing.
Of course, plenty of people do have plenty of time to read HOWTOs and hardware compatibility lists and so on and still enjoy doing so- more power to them. Especially if $200 (or whatever) is still a meaningful amount of money to them that they need for other things. But I've always felt that a big reason why so many people advocate that approach and present it as a rational choice is because they themselves enjoy doing that and would do it anyway regardless of the time/money tradeoff.
I don't think Linux has that much of a hardware compatibility problem these days.
I've built several intel PCs over the last few years without ever researching hardware compatibility and every one Just Worked with a basic Ubuntu install.
Integrated wifi, and even AMD graphics cards are supported out of the box.
I've got an AMD laptop with AMD graphics and have to install the Catalyst software to get responsiveness from Ubuntu graphics. If I don't completely uninstall and purge Catalyst before allowing system updates, then reboot using a custom boot command, then shut down and reboot (with the custom command again), and then reinstall Catalyst, I end up with a machine that boots to a black screen and is essentially useless until I wipe the drive and reinstall from scratch. With 15.10 I thought this had changed with a new set of non-Catalyst drivers, but the problem reappeared.
I hadn't expected this, as my previous two Dells with Intel or Nvidia graphics hadn't caused any problems since years ago when wireless issues got sorted out. Linux has made a lot of progress with hardware compatibility, but if you find one of the weird issues it can be damn near intractable and user forums are a maze to sort through.
Home built PCs are generally not a problem since they all use common, fairly generic, parts. Laptops on the other hand tend to rely more on custom hardware and solutions.
Of course, plenty of people do have plenty of time to read HOWTOs and hardware compatibility lists and so on and still enjoy doing so- more power to them. Especially if $200 (or whatever) is still a meaningful amount of money to them that they need for other things. But I've always felt that a big reason why so many people advocate that approach and present it as a rational choice is because they themselves enjoy doing that and would do it anyway regardless of the time/money tradeoff.