It's actually a criteria to revoke immigration status for immigrants to be on public assistance.
No idea why they don't enforce that more strongly. If I was running things the first thing I'd do is run every list from medicaid to section 8 and food stamps and fire up the deportation machine full speed.
It doesn't matter if it's only a state program from a blue state either. It's the immigration statutes that prohibit being a "public charge", it doesn't matter what government entity is supporting them.