Why is Buddhist art among the earliest art in India

Sometimes things fall into place, even without you knowing that there is a gap. We have all heard about Indus Valley Civilization, and the art-work from there. What Indian art is the next you hear about - Buddhist art. What happened to the intervening 1500 years?

Here is a plausible explanation:

1. The civilization in India between 2nd millenium BCE and 5th century BCE focused on text rather than visual art. The following texts were written during that time (Vedas, Upnishads, Puranas, and the two great epics)
   
   
2. It is possible that much of art of this period was made out of perishable material, e.g. wood.
   
   
3. Some of the art that we consider to be post 3rd century BCE (e.g. Ashok's pillars) may have existed prior to Ashok; Ashok transformed them by inscribing on them, so now they are considered Ashok's pillars, and therefore Buddhist art.