So, by the same logic let me put a question.
Prime minister has 90 ministers in his govt as of today. And he can't be going into all the ministries by himself but it is PM's duty to ensure all the ministers are doing their job, so its ministers who will be taking care of their respective depts and when they are required to travel to places so why can't they travel by sleeper class trains, or govt bus or any other govt transport except air.