Git commits get rebased, squashed, cherry-picked and edited retroactively, written during pair or mob programming sessions or rewritten during code review. And we also know that commit messages often suck. As a result, commits almost never tell you the full story about who exactly contributed, in what order or why.

The process is even messier when writing new bills. They get passed around between different departments, discussed & edited in various committees, etc.

Sure, you could force all participating parties to use git, prevent them from force-pushing or rewriting history even on their "feature branches", get them to sign their every commit, etc. But what you'd then likely just end up with is most negotiation & editing happening out-of-band.

Besides: At the end of the day it's the (majority of the) parliament that enacts a given law, so in my book they are all responsible, even if in practice laws get written by a small subset of people.