Republicans are filing lawsuits as shameless political stunts. Individuals like Garrison can now opt out of the program, and therefore he has no legal ground to stand on. As for the attorneys general, they can only speculate that the program will negatively impact their states, and speculative injury has no standing in court.
The Biden administration's arguments are full of statistical lies and are morally bankrupt. One study estimates the total cost of the program to be a staggering $1T over 10 years. Millions of non-college graduates - who make far less than their degree-holding counterparts - will be footing the bill through rising inflation and taxes.