Agricultural subsidies are one of the weird parts of countries economic policies. Simply put, nearly every single developed country has them. And nearly every country agrees that 'in the long run we should probably get rid of them', but then also agrees 'realistically, nothing will budge, so we'll ignore it as much as we can at every WTO (previously GATT) meeting'

And the reason why they continue to exist, and will probably continue to exist is that there are relatively few farmers in each of those countries, who make up incredibly homogenous democgraphics within their election ridings. Government that even proposes eliminating the tariffs will lose their rural seats/votes/whatever. Every single one of them.