I think you have identified fairly well why the K-12 system is functioning as it is in the U.S. in relation to 1:1 programs. I would add a couple of additional comments that may help with perspective.
The first is that I think what you are seeing in the lack of detail comes from a number of conditions. In K12, we are desperate. Because we exist within a political body, desperation can drive schools to need to seem to "not be behind" our neighbors. That is the key reason this is exploding. Secondly, we are desperate for results - and if someone has sold us a promise of results, we don't dig deep to verify the promise.
Largely, superintendents and school boards know this issue at a fairly superficial level. I don't mean to insinuate anything about intellect, but they rarely dig deep into the research or into framing this question the right way or any other processes which would lead to deeper understandings. As a result, many school districts are making a decision with a superficial-level belief that, in general, 1:1 will lead to higher engagement, personalized learning, more authentic learning experiences, 21st century skills, and the list goes on. I do think decision-makers have a general belief that the technology will transform classrooms, but few schools define performance measures and follow-through with the work needed to continue to drive something towards a set of end-goals. (To often, the gather anecdotal evidence or survey data after the fact - and that stuff generally trends positive).
In fact, I am very, very concerned that we are putting a lot at risk for education by not doing some of the things you have pointed out as lacking in the proposals you have seen - we are potentially putting ourselves at odds with partners at a time when support for public education is a little hard to come by. Additionally, we potentially put our schools at odds with parents and community (although most school systems with 1:1 initiatives are getting a pass due to the superficial beliefs I mentioned above).
Clearly you have not given schools a pass.