If you think abstractly, it will make sense. But I'll make it make sense to you:
AC is what's expected in the US no matter what background you come from. If you're taking a train, whether it's a subway, Amtrak (which is ~ Vande Bharat), local train, whatever, the basic expectation is it will be AC. In India, the perception here is that "low caste" people are treated differently than "high caste" people. It doesn't matter that there's poor "low caste" and poor "high caste", and rich "high caste" and rich "low caste." The perception here is that everybody poor is low caste. The basic expectation we have is that everybody will get AC. For India to make AC a class thing simply perpetuates this idea that your birth determines your social status