Actually, efficacy is not itslef a goal of insurance companies--they only
care about customer satisfaction. To the extent that comes from effective
treatments, that's good; but if it comes from worthless treatments that
cost less and satisfy the customer because of placebo effects, that's
even better as far as the insurance company is concerned.
Yes, there are some recent studies showing that manipulations can in
fact help some back problems. Chiropractors who stick to that, and
who work on research to prove it really works, are doing good work.
There are still chiropractors, though, who treat organic diseases with
no understanding. Hell, it's only been in recent years that the
major chiropractic organization officially accepted the germ theory
of disease.