It's funny, people speak as if decentralisation was a good thing, but very few bother to explain why. Typically, if you dig into it, they cite advantages that you can already get from good old permissioned distributed tech. The only thing that decentralisation gets you (at enormous cost) is that it's harder to regulate.
You need to get out more.
If you are, I am already laughing.
Github is nowhere near the world's "central and only" service for Git, so what am I missing to not laugh about?
The downside of a global distributed database (no matter what) is the speed of light, if you need ordering in any transaction you are in trouble, and no classic service requires that for all transactions in its scope, we figured out partitions, row locks, and shards a long time ago.