Most people can't be bothered to choose a domain, set up a web and e-mail servers for it (because if you're doing it, you gotta do it right) and then maintain it all. Even though it's on almost everyone's todo list, I'm sure.
Setting up a GitHub profile and posting a few quips on Twitter is almost effortless. So that's what we use. If someone comes a long and makes a competing product that is just as easy to use, people will switch. It won't be much of a problem.
GitHub got content creators in the door by being easy to use like that. It became the de facto search engine for users looking to find projects because once you have a critical mass of the creators, that's what happens.
If whoever comes along with a competing product runs it in a centralized manner like GitHub, then they'll create the same issue the OP has with GitHub. If they offer a decentralized, easy to use solution, they need to also offer a way for the person looking for a project to search the decentralized net. Without a unified search, nobody is going to oust GitHub from their spot.
It's not just the setup, it's having to monitor and update the servers, deal with outages, etc. Not to mention you are paying for the machine. For most people this has no inherent value over just letting Github do it.
Setting up a GitHub profile and posting a few quips on Twitter is almost effortless. So that's what we use. If someone comes a long and makes a competing product that is just as easy to use, people will switch. It won't be much of a problem.