The problem is that if you aren't guaranteed some payoff (in terms of publications that will make it possible for you to get more grants and continue your work)

The problem is that if you aren't guaranteed some payoff (in terms of publications that will make it possible for you to get more grants and continue your work) from your work developing the experiments and getting the data, what's the incentive? It's not about being greedy (though there are certainly examples of that) but about encouraging good science. And I don't think people are worried about the internet hive mind, they are worried about their competitors who did not get the grant to actually collect the data.