It comes down to a question of trust and expertise. The PB team at CL have used PsB for almost 3 years, if a ban was picked up PBB during a game we have no knowledge of the veracity of that ban or the system PBB uses.
Furthermore, we have to draw a line somewhere, saying to people you can if you want to or not, does not keep a standard level of play. Using one AC provider we can monitor ban lists, bans etc... we do not want to go down the road of bringing every AC system onboard, and to be fair to all players if one chooses to stream to PBB then all should be, we have neither the time nor the manpower to achieve this aim, and personally I wouldn't want to.
This is not written in stone and in the future it may change.