I Want to Use Solar Power

I have a question that has bothered me for ages and that is why are governments covering good growing acreage of fields in solar panels when they have 100s of 1000s of acreage of wasted space of house roofs that could be used instead . I live in a rented property as do thousands of people so cant use solar because the house does not belong to us and our landlord wont pay for it .However if the government paid for every roof to be covered they would make the money back from excess power returned to the national grid that is not used by households .This seems common sense to me rather than covering good farm land with panels .