This started as a comment in response to Paul's post, but it got out of hand, so I'm giving it its own post.
Since when did the government stop giving teachers (albeit loosely-defined) lesson plans? That's what NCLB and district curriculum standards are all about, Charlie Brown. At my job right now I'm the process of proofreading thirty teacher-written essays about leadership, nearly all of which touch upon the conflict between educators' desire to create new and presumably more effective and creative curricula and the government's insistence that students learn a prescribed set of skills. Obviously this conflict originates more from the state's testing requirements than content requirements, but the two are tightly linked. The problem isn't the state's lack of guidance but their failure to provide it in a useful way.
I don't think any one of your three hypotheses is correct. First, it's not the public's (i.e., the state's) obligation or business to create specific curricula or lesson plans. The government isn't famous for being good at specialization. That's what experts, usually in the academic or private sectors, are for. (As the benefactors of public education, however, the state is entitled to create minimum educational requirements akin to AYPs, provided that, unlike AYPs, they are developed by and for educators and not to sate an uninformed public who has been falsely convinced that teachers aren't doing their job; and provided that, also unlike AYPs, the state provides schools the resources necessary to meet those requirements.)
Second, teachers as a group aren't more likely to be want to be independent than the general public. In fact, in my experience, they're more likely to work collaboratively with their colleagues across sites than, for example, computer programmers (probably because lesson plans aren't proprietary [yet], whereas software is). Teachers LOVE to share and collaborate, even if they can be defensive about their time-tested techniques.
Third, along the lines of my first argument, we should be wary of the government dictating lesson plans. When you refer to the push for teachers to be more autonomous, who is doing the pushing? The state? If teachers are feeling alienated, it's probably because of and not in spite of government dictation of education.
I think the lack of widely-utilized lesson plans is more logistical than deliberate. For one, there aren't many national or regional networks of teachers who can work collaboratively to share ideas and classroom tools. Teachers are notoriously slow to adopt new technology, and many haven't picked up on the idea of chat rooms or blogs where they could formally or informally exchange lesson plans.
Further, many teachers probably believe—with good reason—that one teacher's lessons won't directly apply to her classroom. Demographics, geography, rural v. urban setting, gifted v. special needs students ... any of these factors might render a generic lesson plan useless or unadaptable. It's natural to think, "That plan worked for Miss Brown's class, but all her students' parents are upper middle class, and my audience is working class." We lack a wide-spread networking system that connects teachers of similar backgrounds together, so inter-professional commiseration is hard to find.
Lastly, what constitutes good pedagogy is always changing. More research yields more (and presumably better) ideas, so lesson plans (like software) quickly become outdated and appear naïve to future users. Certainly some principles transcend generations, but there's an understandable desire to always have the newest (read: best) information.
If the problem is logistical, so must be the solution. My employer, the National Writing Project, is just one of the aforementioned national networks that acts as a community wherein teachers can exchange ideas and lesson plans. NWP focuses on both providing the technological infrastructure for this exchange and on encouraging teachers to utilize this technology. They connect teachers with similar geographic and demographic constituencies through national and regional programs. Their teachers-teaching-teachers model makes would-be defensive educators receptive to new ideas because their instructors are peers, not distant legislators. But NWP is just one little group, and, while they are federally-funded, the government's NCLB standards make NWP's job as difficult as humanly possible. (Oddly enough, in spite of NWP teachers' tendency to dismiss the value of NCLB, NWP-influenced students do better on state-mandated testing.)
If the NWP model could be replicated on a larger scale, if it could be not just endorsed but facilitated by the state, then indeed the government could remedy this continual reinventing of the wheel. Rather than enlist bumbling and uniformed U.S. senators to do the job, though, the structure and content would have to be generated by teachers themselves. If the state could magically replicate the ease and resourcefulness of a private company—to harness the brilliance of that teacher who sold her lesson plans on teacherspayteachers.com—rather than futz and stall the way governments like to do, we might have a pretty amazing system on our hands.
And yes, for the record, a raging liberal did just suggest that the government try harder to emulate the private sector. Ha!