Caste persists because it is a sacred notion, not a physical barrier.

Evidence

Why is it that a large majority of Hindus do not inter-dine and do not intermarry? Why is it that your cause is not popular? … There can be only one answer to this question, and it is that inter-dining and intermarriage are repugnant to the beliefs and dogmas which the Hindus regard as sacred. Caste is not a physical object like a wall of bricks or a line of barbed wire which prevents the Hindus from commingling and which has, therefore, to be pulled down. Caste is a notion; it is a state of mind. The destruction of caste does not therefore mean the destruction of a physical barrier. It means a notional change. — Ambedkar, B R, Annihilation of Caste_ The Annotated…, 950

Categorization

• DEFINE: ‘Caste is a notion; it is a state of mind’ — the key reframing, distinguishing physical barrier from mental construct.