In fact, when one looks for them, there are evidence for migration.
Quotes from Romila Thapar quoted in Vishal Agarwal — Romila Thapar
Attribution
Quotes and notes from Wikiquote: Romila Thapar (page history), available under CC BY-SA 4.0.
Quotes and notes from Wikiquote: Romila Thapar (page history), available under CC BY-SA 4.0.