"Power plants may be located in any area where they do not interfere with and are not incompatible with residential, recreational, or other public uses of the Bay and shoreline, provided that any pollution problems resulting from the discharge of large amounts of heated brine into Bay waters, and water vapor into the atmosphere, can be precluded."
You point is a valid, and I don't defend the BCNC, just note that they try to regulate everything.
Light can travel 300km in a millisecond. Being closer to users doesn't seem to outweigh the extra difficulties in plumbing, power connections, network connections, risk of sinking and stormy weather. The potential for mobility doesn't seem that useful either when you need a port with exceptional power and network connectivity.
My guess is that these are not permanent structures. Barges are not particularly suited to harsh open ocean conditions, and as others mentioned, there are some pretty heavy regulations against 'building out' into the bay. The secrecy of it hints at a marketing ploy.