You make that comment sarcastically, but git has in fact made decentralized development easier, and is in fact used that way by some projects such as the Linux kernel.

That many people choose to use it though centralized services such as Github doesn't diminish its power as a tool for decentralized software development compared with earlier tools such as cvs and svn.

Likewise, Bitcoin and Ethereum also enable decentralized coordination that wasn't previously practical, and the fact that accessing them via centralized middlemen is currently popular doesn't change that.