Real time access to laws as they are drafted is a Really Bad Idea. Good ideas need time to incubate. The system you want would lead to the sound byte version of legislating.
Plus, fine-grained version control doesn’t imply real time updates. It’s fully possible to only release the version history to the public after the law is approved.
Good point, but if they used a distributed version control system, lawmakers could have any number of private repositories on which to craft laws before they're merged to the public master repo.
(I wouldn't expect lawmakers themselves to use git, of course; their staff would do this for them.)
Only a better system