They can't be "too rich" where they are financially retired (they are not going to be in the same motivation level) but at least have some disposable income to engage in such an activity. It's a self-selecting network.

Why do people pay $150k to get an MBA at Harvard if you can pay $20k somewhere else and maybe get the EXACT same education? It's because you know 99% of the people there paid $150k and you have a "better" network.