It's almost impossible for them to figure out how much alternative care substitutes for conventional care. Are people who use these therapies seeing their physicians for the same disorder? Are they seeing them less? Are they getting fewer tests?
We have a very fragmented (healthcare) system. The money may be spent out of one pocket, but the savings could go into a different pocket.
These companies are not expecting to cut costs, they're offering these benefits just to cut down on turnover, attract people and keep them.