It has to be something easily adopted for the masses; something not cumbersome to wear and also affordable with practical uses. Part of it was waiting for technology to evolve with it, Qualcomm was finally able to make a chip set for smaller form factors this year which will be used in niantics open sourced AR headset if I'm not mistaken. Give it some time, this isn't something that can be rushed. Also on your full immersion comment, that isn't something that will be easy. It involves the human brain which we are still figuring out; I'd be surprised if we even get proper full immersion in my lifetime like SAO.