There is a wide array of stereotypical reasons that potentially explain why people are not willing to “do” six sigma projects. For example, in some situations, there are no incentives to offset the added risk and responsibility. As yet another example, it is well known that a lack of dedicated resources can deter seasoned veterans from accepting the challenge of a Black Belt project. There are so many reasons that could potentially explain your problem. In fact, there are as many reasons as branches on a tree. You simply have to separate the “vital few” motives from the “trivial many.”
Perhaps the fastest way to a solution would be to attempt “guessing” the right answer. Of course, we all recognize that this approach is not a viable alternative. Although it might take a little time, you should consider the design and execution of a Pareto study. It would seem that this type of investigation has the potential to constitute a more assured path to the root of you problem. To execute such a study, you simply identify the potential reasons why people will not do a project, design a survey instrument to interrogate these reasons, deploy the questionnaire, tabulate the results, analyze the data, and find out why. In other words, let the data do the talking. Let the data lead you to the solution. The approach does not always work – but it is certainly far more effective that “guessing.”
In summary, let me proclaim just one last thing. Firmly stated, my belief is that leadership is the leverage variable when it comes to the success of Six Sigma. Time and time again I have seen this play out – the absence of a strong leader opens the door of failure. A group of people working to a common goal can survive just about anything – except not having a leader. This is especially true of the application projects you briefly mention in the body of your question. Without leadership, all is for not. Leaders are the glue that bond people’s dreams and aspirations together. Leaders create the synergy that ensures the whole is greater than the sum of parts. Simply stated, leaders adapt and improvise — they turn liabilities into assets.
Always recognize that an answer is preceded by its question. Given this, we now recognize that an answer is dependent upon the question, not the other way around. Therefore, it can be said that A = f (Q), where A is the answer and Q is the question. Based on this inextricable relationship, it would occur to me that leaders should be consumed with the design, detail, and delivery of questions, not the provision of answers. To lead is to question, and to follow is to answer. If you seek power, create the question. If you seek praise, provide the answer. A good leader instinctively knows when each should be dominant.