It's a little more complicated than that.

Orcas are socially complex animals, with each pod often having distinct behaviors and vocalizations. To use an anthropomorphic term, orca pods can be said to have distinct cultures. You can't introduce an animal from one pod into another and be assured it will seamlessly integrate; you have to find the animal's original pod.

The rehabilitators never found Keiko's original pod. Instead he was released near a random pod of wild orcas with hopes he would somehow integrate. It was the orca-equivalent of taking some WASP from the American suburbs, dropping them into rural Afghanistan, and hoping it would work out.

It didn't work, so Keiko remained solitary with respect to other orcas. It's no wonder he sought out human companionship; orcas are social animals, and he had years of positive reinforcement around people. Worse, John Q. Public sought him out, further strengthening that relationship.

If we wanted to try again, the best candidate (assuming she's healthy enough) would be Miami Seaquarium's Lolita. We know exactly which pod she came from and where they are--they're one of the best studied pods in the world--and when a vocalization study was conducted, IIRC, in the 90s, she still recognized their calls. Quite frankly, Miami Seaquarium could contribute more to orca behavioral research by supporting such a project than they ever have because it would give us a chance to see whether or not an animal separated from its pod for decades could successfully reintegrate. Would they accept her? Would they take care of her? Would they teach her to be a wild orca again? Answers to such questions would tell us a lot about their capabilities as animals.

(Source for information on Keiko: As an undergrad studying Animal Behavior, I attended a seminar on the effort and failure behind Keiko's rehabilitation, held by people involved in it.)