That is closer to the historic model popular in the '80s, say, with companies like Sendmail and the commercial backers of the BSDs. Though, in those cases the support is focused on a very small target.
The issue is that providing tier-1 support to "everything we can cram on a DVD" is that it is basically impossible. While "Gnome" might be a pretty solid box internally, a given snapshot of "Gnome" might only really work with a specific combination of kernels and userspace utilities. Consider the various layers audio, or network configuration, needs to touch. And consider non-Gnome, Gnome apps, like GnuCash for example. It doesn't work with the latest versions of Gnome.
Sure, you can get it to work, but it doesn't "just work". Getting it to work in many cases might take a lifetime of experiences. You can't possibly build up a knowledge base of quick solutions to common problems if you don't make efforts to control the source of the problems. So every tech support call is about actually debugging a problem, rather then giving someone a quick canned answer. So all of your support calls are an hour long (or longer), and require someone with years of experience to handle.
So instead of having a call center filled with people who have a loaded cost of $15/hour, and answer questions in an average of 5 minutes, you need a call center filled with people costing $75/hour, and who take an hour to answer calls. You do the math on how much a subscription to such a service would cost.
It does happen, but they are called consultants, not distributions.