Lean Sigma Thoughts

I've recently been going through some training on the Lean Sigma methodology. It's all about Process Improvement and it employs the DMAIC (or DMAEC) steps: Define, Methodology, Analyze, Implement (or Engineer) and finally Control.

It's a very sequential model (not unlike a waterfall software life cycle methodology) with tollgates at each step. It's pretty interesting and I'm learning a lot of academic material. I'm doing my Green-belt training and I am using the textbook material on an actual project that is causing my boss pain. However, as I've been digging into the project, I've discovered that a lot of the steps were carried out 2 years ago on much the same pain points. In fact, there are reams of documentation all the way to the Engineer Phase. The solution was never implemented however. Now there's a big project underway (of which I'm working on a very small chunk) that is looking at the same issues again. So my question is: why? Why will the result be different from last time? Why wasn't the last solution that was brought to the table 2 years ago not carried out?
Heck, we can do a Lean Sigma project on this question alone!

And furthermore as I was digging into the items, I started getting innovative ideas. What if we could do this or that? and implement it with a small group? If it worked, we could spread it to the other groups. And then it hit me. The Lean Sigma process to some extent is devoid of innovation! That flash of inspiration; that 'hmm, what if we tried this?' is somehow lost along the way. A practitioner can so concentrate on each one of the steps at a time that s/he never sees the issues holistically. The emphasis on only defining a problem or measuring or analyzing precludes the 'what-if-we-did-this?' The problem is engineered to death.

In this project I'm on, the solutions proposed from the last go around made sense. I have a feeling that the stakeholders involved were change-averse to implement some of the bigger changes and didn't want to rock the boat. I also feel that our Lean Sigma group is seen as 'outsiders' or consultants who come in, do their thing, drop you the results and leave. Their stuff is good but they're done and they're off to the next thing. Stakeholders might like the analysis and agree with some of the solutions but they take a risk when implementing. If the proposed solutions don't work out in the stakeholder's favor, the project manager is left holding the bag. When Lean Sigma or management consultants leave, the project manager (who may have contributed to the development of the project) is not invested in the solution, so will be less likely to implement it (at least from the e.g. I've seen).

Again, on this particular project, I saw comments from one of the stakeholders who more or less shot the proposed solution in the foot. The Powerpoint slides depicting the proposed changes were passed around and then the stakeholder fwded the slides to his managers with many more criticisms rather than favorable remarks. It's no wonder the project stalled. What top level manager would give the go-ahead if their employees thought there were unresolved issues?
Questions:
1) Why wasn't the solution developed jointly with the stakeholders?
2) Was there a chance to rectify/address some of the concerns of this particular stakeholder?

There've been tons of issues with this particular product line; everyone agrees it is broken; The product line manager is definitely risk-averse and doesn't want to do anything drastic.