It's not necessary, it's a waste of development time and easily the biggest big-picture collective failure of our software engineering profession of the last decade. It easily beats out anything from the $foo.js world and the ongoing low-level security nightmare of web application development, because git, and more importantly, unnecessarily complex and error-prone git workflows have seen adoption across all kinds of software. There are probably a dozen projects in the world (the kernel admittedly being one of them) that are justifiably a good fit for the complex git-native workflows that have become standard practice across the industry today.

But if you're doing it the old-fashioned way, you might as well use Subversion. Or mercurial, if you want all the local history, with the added bonus that unlike git it sensibly keeps the least-surprise semantics of 'commit', 'revert', and other commands that merely have a 30-year history of expectations that held true prior to git. But Mercurial was not authored by Linus, nor does it have the impenetrable, otherworldly data model that a first-time version-control-system author would unavoidably end up concocting in scratching their itch without consulting the existing, completely satisfactory, solutions that served us well for decades, which greatly reduces the number of interesting topics you can blog about for Mercurial.

And so, git sees the adoption, github gets the $2bil valuation, and even bitbucket ends up switching to git as it's default. It won.

Software engineering, collectively, has a lot of maturing to do.