Most people don’t want to share their process with others because of fear. People that are fearful or in a high-blame environment do not want to share, because they don’t want to be caught in a “Gotcha” moment.
The environment can make employees territorial. If you want people to share, you need to address their fear. You have to make sure to tell people that it is about the process, it’s not about finding fault or a witch hunt, and, stick to your word!
Acknowledge that the process is not designed optimally and that the people in the process are the biggest victims of that. Make it OK to share what is messed up about the process, because those who don’t want to share are just avoiding the hall of blame!