There is one overriding reason this is a bad idea: it gives the government direct power over the voice of the newspaper, without running afoul of the First Amendment. If the legislature decides that it doesn’t like the paper’s viewpoint, it can pull the subsidy and send the publication back into bankruptcy. The mere threat of this will cause the editors to tread lightly on issues that may cast aspersions on their sugar daddies, i.e. the elected officials who write the checks.
It’s one of the worst remaining loopholes in free speech jurisprudence, writ into law by Rust v. Sullivan (1991): the First Amendment does not prevent government censorship when the government pays for the program that facilitates the speech it wants to regulate.