not all policies cover it. I had to change insurance companies to get it (fortunately, my employer had several options), but I had to go with the most expensive policy they offered. I stayed on it for two years, I think (in case there were issues...), and then switched back to my original policy. Five years later, of course. all of their policies covered it...oh well...
anyway, it's not an issue with BCBS. It's an issue with your employer. Most insurance companies actually DO have a bariatric surgery rider, but employers can pick and choose which things they want to include in the particular policies they offer to their employees. I was told by our HR dept that it was pretty expensive to include bariatric surgery coverage, so they only covered it in their most expensive (to the employee, that is...) policy.