What is the nature of your industry? Is it that the group has companies from various industries? What is your designation? Will you do this study alone or you will assist some senior?
Reasons for poor response to the internal job vacancies could be many. However, poor response is reflection of your company's culture. You need to find out whether there is absolutely uniform culture across the group or sub-group plays it's own tune? If it is so then person working in some other sub-group may not like to take risk. He/she would prefer status quo.
MNCs in particularly American MNCs, have strived for bringing uniformity in their culture. Take the case of GE. Be it GE Medical or GE Power or some other SBU, GE has uniform culture in toto. This helps GE to transfer a person from one continent to another, one SBU to another.
The second reason could be lack of job rotation. You may promote job rotation within the SBU itself. Probably Managers in your company have institutionalised with certain way of working. Now they do not want to change this mental alignment.
The third reason could be lack of career consciousness. Do managers have die-hard ambition to grow to they prefer moderate growth?
One more reason could be lack of career planning. For how many managers career plan is made? If it is made then who has made it and on what parameters it is made?
To find out poor response to internal job vacancies, you need to take survey. You need to find out the reasons by asking few direct and few indirect questions.
22nd May 2016 From India, Bangalore