It's cheaper, far safer, reversible, and adjustable, and in many areas is done as an out-patient procedure. And whereas weight
may be faster with gastric bypass, over time there's no difference -- in fact some people with bypass start to gain after time. If that happens with banding, the band can be tightened (it takes a few seconds, injecting fluid into a port under the skin). With bypass, you're mostly out of luck, or need a huge procedure.