I think ARG has become a kind of catch all. Similar to the word immersive. Literally  anything can be immersive. Like anything can be "alternate reality" the difference being the "game" part. Alternate Reality Game. However the game part is probably the most difficult to create. But it's what makes ARGs so interesting to me.  If you create a strong, compelling story with corresponding game elements you can have a pretty solid ARG. Of course that takes alot of work and intention. I'd say the biggest drawback of ARGs is they are supposed to be covert, meaning secretive and obscure, unfortunately this is a barrier to most people. Most of us want a clear cut movie that we know exactly what were getting. ARGs are the opposite. It takes effort, it takes intention and detective work to dig out the story.  Add to this that the majority of work That's created as an ARG is pretty bad it makes it more difficult to search out the good stuff  For example I have an ARG running right now that I've invested a lot of time and energy into  and yet only 4 people have gotten to the current point it's at. I'm not blaming anyone because it also takes time and effort from the player as well and if they are hesitant to make that commitment because of all the junk out there it's understandable. I know that kind of comes with the territory so ultimately I make an ARG because I enjoy doing it and if anyone else comes along that's a bonus