Often when I am making dinner, the cat would want to know what I am doing. If I ignore him, he usually gets more insistent and annoying.
So I simply show him or let him sniff at the carrots (or onions!) I am chopping up. He then knows what I am doing and loses interest. (Or if it is meat, he gets more excited and then I have to give him a bit, or give him his food.)
It is the same thing with business process work. People are curious by nature. Especially if they suspect what you are up to has impact on their work and lives. Fostering involvement and buy-in is as simple as letting everyone who is interested have a sniff.
You don’t have to give trade secrets away. You don’t have to respond to their reactions – unless they are the primary stakeholders. I don’t always give the cat what he wants, but if a dinner guest (primary stakeholder) says she is allergic to onions; that is a different matter.
Often the default approach in business process projects is to keep everything secret. The transparent approach is to make available everything (except the missile launch codes) to everyone who could conceivably be affected by the project.