It's not even just this. The scripts that are on the server right now are designed for use on a single server. Things like the car shops, regular shops etc just wouldn't work across multiple shops. I believe the example was bought up before of going to buy a car, going to get the money out, and by the time you come back someone else on the other server has already bought the car.
Also things like the gangs, how can a ~35 man gang split up it's leadership between two servers, and stay consistent between them. Say the members on server 1 wanted to attack another gang, what would the gang on