Why public parameters generation ceremony was not open for anyone?

[xor]

I love the idea of zcash. However, I am disappointed by the public parameters generation ceremony. I expected it to be open and to have more participants.
Why participation in the public parameters generation was not public? Why use only 6 people? If I had a chance to generate a part of the secret myself, destroy my part, and verify that it was actually used for the final result, then I can be sure that the system is legit in that aspect.
I understand there may be issues with people not performing their part, but it can be solved by asking people to make security deposits in Bitcoin, and returning them in case of success.
Were there any technical difficulties not allowing to perform an open MPC process with several thousands of people participating? Any other considerations?

[CCQ]

How to generate SNARK parameters securely

The messages that have to be passed from one node in the Secure Multiparty Computation to the next node are on the order of gigabytes in size. And, if any node fails (stops responding), the rest of the nodes can’t make progress without it, so we’d have to kick that unresponsive node out of the Secure Multiparty Computation set and restart the protocol. So, for a bunch of practical operational reasons we can’t handle lots of participants.