Diet and exercise generally do not cause substantial long term weight loss

There is a pretty serious selection bias in that study.

I know some people who lost a noticeably amount of weight and kept it off. These people did NOT go to any structured programs. They just did it themselves.

I suspect that those who are capable of losing (and keeping it off) weight by themselves just do it and do not show up in the statistics of the programs analyzed in the meta-study linked to. These structured programs select for people who have difficulty in maintaining their weight and so are not representative of the general population.