Dear Wordpress- meet MVC, git, postgres, sane security and 100% testing. Please leave your old friend FTP- he was never all that safe or great to begin with.
The thing is, Wordpress is used by people who don't know and do not want to know what those things are.
I dare say, even PHP is mostly used by people who don't know what most of what you wrote is.
I've seen even Magento forum members (Magento being a complex e-commerce solution written on the Zend framework) saying they do not know how to write more than a couple of lines of PHP.
FTP: lots of graphical clients available for all OSs, your host can probably give you a bookmark to drop into one for a Windows client and a Mac client, and if they don't it's pretty easy to make a new bookmark pointing to your server with your login/password. You're done, start uploading stuff!
Git: Hi! Let me teach you about version control! We'll start with the command line version. Also you may have to ask your host to turn on Git access to your files. And the likelyhood of them making it easy for you to just drop one file into a simple graphical Git client is close to zero.
Who in your life is clueless about computers? Imagine you're them.
Which one looks more appealing? Which one looks scary and intimidating and demands that you learn a thousand new things on top of learning all the stuff you'll have to learn to get a website up?
To be fair, Git is probably arcane to quite a few 'technical' people as well, and a lot of the people who do use Git probably fall into the set including myself who would be lost beyond the basic 'init, add files, branch, merge, push to remote' stuff.
I think for basic functionality, we still have a long way to go with Git clients.
There's no reason we can't make a Git client that's as simple to use as FTP, and obscures advanced functionality completely unless a user asks for it. Github's desktop clients still aren't quite this.
I'm sure someone would ask why use Git at all then if you're not going to be branching/merging all the time- but at least then when I (more advanced person) need to come in and fix someone's site, I've got a good place to work from, even if they've always just committed linearly to a single branch.
I was helping a designer-only friend of mine with the implementation of a basic website theme. After an hour of trying to talk them through how to use the github app (let alone git command line) I gave up and we just used dropbox.
The point being, sadly, I think that we're a ways off before the average non-technical person is comfortable using git.
FTP is a vastly simpler process to accomplish what it does -- transfer files from point A to point B. And if all you would be using Git for is, essentially, pushing the contents of a repository to a remote server, then it can sort of be akin to driving a Lamborghini Murcielago around to the corner store.
How is that going to help when over 10 million people are running WordPress on shared hosting accounts where MySQL and FTP are the only database and only file transfer options?
I don't see what would prevent those hosts from updating. Its not like installing SFTP and Postgres is that big of a deal (even on a huge deployment, it shouldn't take that long...)
I've seen even Magento forum members (Magento being a complex e-commerce solution written on the Zend framework) saying they do not know how to write more than a couple of lines of PHP.