That is because it is not a public securities exchange. It is a private foundation that has assets. The Foundation has chosen to provide a way to let beneficiaries exchange assets with other beneficiaries. By law, the assets belong to the Foundation. The entire PDR exchange is based on trust that the Protector, Pedro, will do the right thing when it comes to the beneficiaries.
Let's say that I have a trading account and my children (beneficiaries) sign over some stock certificates to me. I give them a receipt saying that they "deposited" them with me. This receipt will not be useful outside of our private transactions. I gave them my word that I will protect their deposits and do what they want me to do with them. It is their trust in me that would make them want to participate. Legally, the stock is mine. However, if I am true to my word, then when one child comes and says that they want to sell some of the stock they "deposited" with me to the other, it is up to me to keep track of the transactions. The brokerage account that I have holding the stock will not have any idea about what is going on. It is a private transaction.
This is very similar to the way the PDR Exchange functions. It all comes down to a matter of trust in Pedro.
