IIT have prestige. If they care about leveraging that prestige and incentivize their graduates to some lifestyle choices there's ways to do it.
One example is the elite French "école polytechnique" (think the #1 IIT equivalent in engineering): tuition is waived, you even get paid a stipend as a student... But if you don't serve in French public service for 10 years after graduation, you have to repay it.
https://programmes.polytechnique.edu/en/ingenieur-polytechni...
> There are no study costs for French students, on the condition that they work for the civil service for at least 10 years within the 20 years following their graduation. Otherwise, they must repay the tuition fees
That would work as a "brain drain" tax.