MotoGP has been taking in new circuits which will challenge the riders to push themselves. Major criteria for keeping circuits on calendar is safety and run-off areas for riders to be safe.
Currently there are two races which are organised in United States of America. Circuit of the Americas and Indianapolis Motor Speedway, which is held in Texas and Indiana respectively.
Previously Laguna Seca was also on calendar and was a track several riders loved to race on. It is currently not in operational purpose, as it is being renovated to meet modern standards of racing.
Now Indianapolis has also been taken out of MotoGP calendar from 2016 season. There is no news when MotoGP paddock and riders will be seen again on this circuit.
Reason for not coming back to Indianapolis during 2016 MotoGP season is not very clear. One of the main reason is the tremendous logistics involved, which is not viable for a single race.
2016 MotoGP season will have 18 rounds and Circuit of the Americas will continue being on calendar. Laguna Seca is expected to be ready in a couple of years and action could return to this legendary circuit.