> Couldn’t we apply the exact same principles of github, but to a markhub (for lack of a name or creativity)?
Sure you could; in fact, I'm sure it would work pretty well. If you look at the StackExchange series of sites, you'll see everything from programming to mathematics, parenting to gaming. There are a lot of sites on that network, all of which provide an excellent resource.
However, here's the key element that would keep 'marketers, advertisers, and product peeps' out: competition.
GitHub works because people are sharing their code. If you worked on a marketing campaign, are you going to release your market research with what works best to your competitors? If you create a product, are you going to ignore patents and release that design/schematic for free?
In a perfect world, the answer would be yes, but a lot of people simply aren't open to the same level of sharing that a lot of developers are. Why did open source software take off, but not nearly as much "open source products?" I'm not sure, but I think it has something to do with the culture of shared knowledge, and the satisfaction of someone else using your work.
You can still make a profit on open source software -- $RHT is an example of that -- but would you be able to do the same if your product itself was open source? I personally think so, but this is why GitHub clones haven't spun up in every possible industry. In my opinion, anyway.