Farm subsidies go back to the War, and the system put in place by the Attlee Government worked perfectly well until the Conservatives took this country into the Eurofederalist nightmare.
Now, those of them who belatedly want out of that, want it in order to turn this country into a petri dish for the utterly unconservative and un-Tory economic theories that predominated, but which never quite became monolithic, during the 40 years between Jim Callaghan's turn to monetarism and Theresa May's loss of her overall majority.
"Why should farmers get State aid when no one else does?" is the wrong question. The question ought to be why other people did not get State aid when the farmers did.
In any case, the likes of Michael Gove are wasting their time. Theirs is the farmers' party. It always has been, and it always will be.
Everyone else in it is just a farmhand, and the terms of their occupancy of their tied cottages have never been reformed. They can be evicted at any time.