Yes it's great for the EU, but not so great for the Mercosur, is it? The EU wants them to buy products from the EU, but if the Mercosur acted the same way as the EU does with regards to agriculture, would mean they would also "protect" their industries from "unfair EU competition" and no deal can be made at all.

If you want to have commerce, you need to give some to get some. Without agriculture being included, the EU would just take and not give anything. It used to work in the colonial times, but one would hope that is behind us now.