There is a pessimistic answer to this question (or is that maybe, the realist answer?) and the answer that an optimist (the idealist?) would give:
The optimist’s position is easy, to begin. Education is a civil right and governments thus have a social, humanitarian obligation to fund education and create an equity of access to the advantages that learning opportunities give to individuals.
The pessimist’s position is just as easy. Judging by the state of education and the social inequities that education structurally reproduces; judging by the nominal funding that the government actually set aside for education; and judging by the broad and deeply entrenched conditions of control that the government have over state-funded education compared to the private sector, the government funding of education is a transparent guarantee of leverage over how education works, who/what it serves, and what sorts of ideological ends and structures institutions of education reproduce.