The state isn’t outside class struggle, so it helps to understand that if they do not serve capitalists, who else could they serve? The peasantry are nearly gone at this point, leaving the petite bourgeoisie, national bourgeoisie, and the proletariat. We struck out the big bourgeoisie, leaving petite and proletariat, and what helps narrow this down is that the well-being of the whole of society is what is prioritized, which benefits primarily the proletariat, and that their goal is collectivization of production and distribution, which hurts the petite bourgeoisie.