Ok so here's the thing - they tried that with Keiko (Free Willy) several years ago. It doesn't work.
Orca are migratory - they move to different areas of the ocean as the climate warms and cools. Keiko's Sea-Pen was considered 'large enough' for natural living. Keiko died from complications resulting from pneumonia... which typically results from the cold.
These orca have been captive in climate controlled tanks, with the best veterinary care and food. They are no longer able to regulate temperature in an ocean where temperature fluctuates. They can't hunt for their food, and you would be removing them from their veterinary care at a time when their bodies would be at greatest risk.
Sea World (and other parks) have admitted how wrong it was to capture these healthy animals and hold them in pens, but they are also smart enough to realise that it is too late to put them back. All they can do now is keep them in the best environment possible, and utilise them to teach others about mankind's previous mistakes.
As a social pod animal, they would die without that social interaction, so the breeding program is also necessary.for their continued health, and those bred in captivity know nothing else.
Just because a crackpot that has never worked with Orca prior to filming thinks we should release them all into the wild, doesn't mean it's the right thing to do.