I already asked this in TWC but so far didn't got answer I was looking for.

This question is firstly for EB Team of course.

Code:
    grain_silo
    }
    }
    grain_silo requires factions { all, }
    {
        capability
        {
        population_growth_bonus bonus 2
        happiness_bonus bonus 1
        trade_base_income_bonus bonus -1
        }
    construction 8
    cost 6400

What is the reason or explanation for income penalty?



Of course I can edit it to whatever I like but... I don't get the logic of the penalty.