Why no creamy layer among the SC ST group

The cure for social discrimination has been the Affirmative action.
In the case of gender based discrimination too, Reservation has been the chosen path. 50% reservation for Women is the highlighting evidence.
    The point is simple and logical. Reservation is the way to achieve Proportionate Representation, that is, to cure the malaise of social discrimination.
   However, the Anti-reservationist have aversion only to the caste based Affirmative action. They make chaotic arguments raising arbitrary questions, most of these questions being of a denialist nature that the Caste based discrimination is an imaginary victimization,  which has never actually occured.
   One of these questions is why should a generation of the same family enjoy the benefits of reservation. The question is more of a sham exercise , perhaps with an agenda of dissolving out the reservation policy altogether. However, if there be any substance it then this is perhaps what it wants to point to, -- why should not there be a creamy layer kind of filtering even among the SC/ST group, just like there is one in the OBCs.
    In my thinking, the reason for why a "creamy layer" kind of internal filtering couldn't not be adopted is settled in the depth of social discrimination suffered by them, which has it's evidence sowed in the Constitution too. The reservation for SC ST is emanating directly from the Constitution, Art 335, Art 338 and Art 338A, (read with Art 17) whereas the OBCs receive it indirectly, through an interpretation of Art 14, when read with Art 340..
    I think the one truth that the anti-Reservationists wish to keep suppressed is that the reservation benefited castes, all, including the SC , the ST and the OBC together make above 80% of India's population. Caste based census data has been kept suppressed for a host of reasons, one being this.
      So, logically, the figures for reservation-in-employment could have been perhaps as much. But then, since the arguments for capping the reservation has been held successful in the Supreme Court of India (for most purposes) , therefore 49.5% max has become the consensus mark. Thus, whereas the SC and ST have 15% and 7% reservation already, a figure which represents their population proportion, therefore the remaining from the cap of 49.5%, i.e. 27%(approx) went into the OBC's favour. However, since this is way less compromised figure compared to their proportionate representation, therefore a mutual contest in the OBC group was to become apparent. It is to resolve this internal dispute from this class, that the 'creamy layer' idea was floated and found its way. 
   The tragic ground truth about the SC and the ST group is that they have still not succeeded in making it to the social resources in many counts as has been kept reserved for them. Many of the seats for SCs and STs go unfilled despite a reservation. That may explain why the Creamy layer kind of idea may not yet be suited for them.