"Grift" not grit. Trump is bad-faith arguing that these public broadcasters offer no value and are just stealing from the public.
In reality this administration just doesn't like them because journalism and facts fly in the face of their misinformation, disinformation, and political propaganda/spin.
I think it could be more tactical than simply not using the correct word. Trump has been a grifter his whole life; selling people things and not delivering on them...entering into contracts and not honoring his side of the agreement.
Being a grifter is a pervasive and consistent theme in his life, so when he accuses others of grifting, it indirectly softens those same accusations when levied at him.