One of the main reasons has to be that there is some mutual benefit, whether that is financial benefit or to ensure a quality or service or some other form of benefit to one or both sides.
Barriers to engagement can be vocabulary people use different "speak", exclusion by other member orgs i.e this is work we do keep out, simply not knowing where to look so maybe communication is a barrier and also we must recognise that for some it is simply not important for them to engage at that given time and they have the choice not to engage
