Good question,
There is a lot to this, as has been suggested by others. Perhaps we should also consider the foundations or principles of the main themes (usually spiritual and 12 step) in rehab, the messages of the Secular programs are not easily re-interpreted through traditional recovery methods and visa versa. In fact much of the drive behind Secular methods is a underlying push against the powerless, higher power, surrender ideas. To be taught methods that in many ways oppose each other would cause immense confusion. I hope one day there will be actual Secular recovery centers open up, with good doctors and science backing up the program. Perhaps at the end of the day we don't really need inpatient rehabs, there maybe some arguments that the institutional system as it exists now is actually part of the problem not the solution.