Because there are a lot of different kinds of workflows, and I don't even know how you'd begin to organize them. I mean, maybe it's not even possible.
It would just be nice if it were more possible to "ease into" Git, rather than feel like you have to go through the equivalent of a college semester learning it.
This is the point where I think it's appropriate to link another front page article: http://news.ycombinator.com/item?id=4338845
I've learned Git about the same way I've learned *nix systems and programming languages in general: piecemeal, a step at a time, on a largely need-to-know basis. It's been 4 years now and I feel like a complete novice, but I rarely need to do anything other than (1) synching local with remote repo, (2) committing a change, and (3) using a feature branch.
Sounds like a great idea for making one type of workflow easy. The great part about Git not having an abstraction is that it supports almost any workflow. You can choose what flow is right for your project.
Which is, by the way, why the documentation is not task-oriented, it's data-model oriented. The same command might be used for two completely different tasks in two different processes.
Other tools that aim to make the basics for committing easy do so at the expense of implicitly supporting only certain workflows. Think of something like Perforce. You don't enforce your process with Perforce, you choose your process so that it will work with Perforce.