I too had this same question and just figured it out.

The route is just coming from the [Route("[controller]")] line. It uses the class name of the controller minus the word "Controller". So, since the name of the class is "WeatherForecastController", the route becomes /WeatherForecast.

If you would change the class name in the line underneath of the main route to WeatherForecast2Controller, your route would become /WeatherForecast2.