Why are there mainly legit talent agencies in LA and NYC?

you don't have to be a SAG member to get a SAG approved agent or to go on auditions for SAG covered work. if your just starting at 16 by the time you get training and experience, unless you look very young, you will be too old for teen roles. that's pretty much how the majority do this. they get to where the opportunities are,get educated and go on auditions while working a regular job. very few make an actual living at just acting alone. Nyc has some tv and a lot of theater. LA has mostly tv and movie opportunities. most of the agents are in those places as that's where the auditions and work are.