Related to the above, participation of even great people is hard to get unless you give them something tangible. This is especially true of those who see themselves as interdisciplinary already. I find that the majority of 'participants' only really get into it if they think they'll get something. Long experience has taught me to count on a core of people who are committed, and to treat the others as valuable resources I'll have to pay for in some way. Another disappointment in human nature.
Successful people are often extremely busy.
Even if committed to an idea, we all have tough choices to make. This makes it really difficult to sign up that member of the National Academy who'd draw better students for everyone or look great on a proposal. Our training grants and IDGPs add to my teaching load, doubling it much of the time. Not everyone has the freedom willingness to slice investment so many ways. My publication rate has dropped WAY off since I got into program development.