Lets take Ubuntu as an example. Today you can get Ubuntu laptops that will work out of the box. Is that true tomorrow? Absolutely not. The next distro version will break something in the hardware. I have been burned by this twice now. At then end of the day the Apple premium is not really a premium. It ensures that they continue to support their legacy hardware for years. The people who bash the premium as some sort of "idiot tax" are actually valuing the software that runs on the machine at 0$. There are too many people in this world that don't understand how much effort it takes to create and maintain good reliable software. You see it on the app store where people can't fathom spending 99 cents and you see it in the bashing of Apple devices.
Lets assume that your hardware works beautifully with the current version. Then you actually look at the apps shipped with the distro. They are poorly made and do not form a cohesive OS. You are forced to hunt for other open source equivalents to basic stuff like "paint". Have you tried using the calculator or notepad equivalents? They suck compared the simple and easy to use Windows and Mac equivalents. This is something even Windows gets right. It comes from the fact that Canonical does not have the resources to build each app around a unified design and UX principle so they farm it out to the "open source community".
Finally, why do each distro version seem to break something on the same hardware year after year? There seems to be a serious lack of regression testing on these distros. For 10+ years I have witnessed how one version of Ubuntu breaks some stuff, fixes others and then the next version fixes some stuff but breaks previous working items. Then it gets worse, the subsequent version breaks previously fixed stuff again! I am forced to QA the entire OS every time a new release comes out and hope I don't miss something(which I always do)!