The funny thing is that git wasn't built to have a centralized host, but that was the paradigm people were used to, and Github was so convenient that the paradigm stuck around. There's no reason we couldn't just `git remote add backup <VPS_ADDR>` to have a secondary host.
>> Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency
As the other replies say, git is already decentralized. What we need is a decentralized way to recognize one of those mirrors as the main one. I think gitchain: http://gitchain.org/ was supposed to solve that.
More like not to entrust single copies of open projects to US-based companies. Even a somewhat 'respected' company as Github is just a corporate body that will bend over for anyone with business and away from anything that is Too Troublesome.