Sure, and so should the president unilaterally give up a significant amount of revenue that was supposed to, by law, fund government programs, those estimates would have to be revised, but then what?
The revised estimates would show not enough money to pay for those programs as expected.
What do you think happens next? Do you expect the government programs to be cut short since the money's just not there anymore?
The #studentloan forgiveness doesn't happen in a vacuum. The revenues from those loans were already committed to supporting programs that would then be underfunded.